【】 Objective To compare the success rate and stability of different doses of complete Freund"s adjuvant (CFA) in rat models of chronic pain and depression comorbidity. Methods Sixty SD rats were randomly divided into control group, low-dose CFA group (CFA-L) and high-dose CFA group (CFA-H), with 20 rats in each group. Rats in CFA-L and CFA-H groups were injected with 50μL and 100μL CFA, respectively. Rats in the control group were injected with 0.9% sodium chloride solution. The general state, body weight, mechanical withdrawal threshold (MWT) and thermal withdrawal lantency were observed at 0, 7, 14, 21 and 28 days after modeling. open-field test (OFT), forced swim test (FST) and tail suspension test (TST) were used to evaluate the depressive behavior of rats. The contents of glutamate (Glu) and γ-aminobutyric acid (GABA) in the anterior cingulate cortex were detected by enzyme-linked immunosorbent assay. The expression of brain-derived neurotrophic factor (BDNF) in the anterior cingulate cortex was detected by immunohistochemistry, and the pathological changes in the anterior cingulate cortex were observed by hematoxylin-eosin staining. Results (1) General conditions: on the 7th day after modeling, the left ankle joint and toes of the rats in CFA-L and CFA-H groups were obviously red and swollen, and the swelling was more severe in CFA-H group. On day 14, 21 and 28 after modeling, the redness and swelling of the left hind foot and ankle joint and toe of the CFA-L group gradually recovered, while the redness and swelling of the CFA-H group were still obvious, and the amount of water and food intake decreased. (2) Body weight: The body weight of rats in CFA-H group was significantly lower than those in blank group and CFA-L group on day 14, 21 and 28 after modeling (P < 0.05, P < 0.05). (3) Pain-related behavior: compared with the control group, the MWT and TWL of the CFA-L and CFA-H groups were significantly decreased on the 7th and 14th day after modeling (P < 0.05, P < 0.05). On day 21 after modeling, the MWT of CFA-H group was significantly lower than that of blank group and CFA-L group (P < 0.05, P < 0.05), and the TWL of CFA-L group and CFA-H group was significantly lower than that of blank group (P < 0.05, P < 0.05). On day 28 after modeling, MWT and TWL in CFA-H group were significantly lower than those in blank group and CFA-L group (P < 0.05, P < 0.05). (4) Depression-related behaviors: on day 7 after modeling, the total OFT movement distance of CFA-H group was significantly lower than that of blank group and CFA-L group (P < 0.05, P < 0.05). On day 14, 21 and 28 after modeling, the total OFT distance and central dwell time in CFA-H group were significantly lower than those in blank group and CFA-L group (P < 0.05, P < 0.05), and the FST and TST were significantly higher than those in blank group and CFA-L group (P < 0.05, P < 0.05). (5) The expressions of Glu, GABA and BDNF in CFA-H group were significantly higher than those in blank group and CFA-L group (P < 0.05, P < 0.05), while the expressions of GABA, Glu/GABA and BDNF in CFA-H group were significantly lower than those in blank group and CFA-L group (P < 0.05, P < 0.05, P < 0.05). (6) Anterior cingulate cortex pathology: CFA-L group had less damage in the anterior cingulate cortex, more pyramidal cells, more arranged cells, clear nucleoli, and a small number of cells showed karyknosis and deep staining. Compared with the CFA-L group, the CFA-H group showed disordered cell arrangement in the injured area of the anterior cingulate cortex, a large number of neurons were pyknotic and hyperchromatic, the number of pyramidal cells was significantly reduced or even disappeared, and vacuoles, red blood cells and neurofibrillary tangles appeared in the interstitial space. Conclusions CFA injection of 100 μL can successfully establish a rat model of chronic inflammatory pain and depression, which can induce hyperalgesia, depression-like behavior changes and changes of Glu, GABA and BDNF in the anterior cingulate cortex, and induce pathological changes in the anterior cingulate cortex, which is consistent with the pathophysiological characteristics of chronic pain and depression.