Objective We aimed to characterize the relationship between the expression of the Alu gene in a model of human gastric cancer metastasis and the degree of gastric cancer metastasis in tissues and organs and establish a molecular biological method for the early evaluation of gastric cancer metastasis. Methods Alu gene expression plasmids were constructed from the genomic DNA of human gastric cancer cell lines SGC- 7901, MKN45 and the normal gastric mucosal cell line GES1. Alu gene expression in various concentration of gastric cancer cells SGC-7901, which was widely mentioned as human gastric metastasis cell line, was measured by real-time PCR. The relationship between different Alu expression of various concentration was measured by cycle threshold (Ct) value to modelling the standard curve. A human gastric cancer cell xenograft metastasis model was established by the subcutaneous inoculation of SGC-7901 and MKN45 cells into nude mice. The expression of Alu in the resulting tumors in the mice (in the liver, spleen, lung, kidney, and subcutaneous tissues) was then measured by real-time PCR, and a curve for the relationship between the expression of Alu and the degree of tumor metastasis in each tissue was constructed. Subsequently, fresh tumor samples from patients with gastric cancer were subcutaneously inoculated into nude mice to construct a xenograft model, and the relationships between Alu expression in the tissues of the mice and the degree of tumor metastasis in the organs of nude mice was similarly evaluated. Results The number of SGC-7901 cells negatively correlated with the cycle threshold (Ct) value for the Alu gene (R² = 0. 9239). In the xenograft metastasis model, the expression of the Alu gene was higher in subcutaneous tumors than that in lung and liver metastases, and the expression of the Alu gene in lung and liver metastases was higer than normal nude mice. This was consistent with the result of histopathological examination. In the gastric cancer patient xenograft model, if there was no visible metastasis in the organs of nude mice, the expression of Alu gene (Ct 17. 86) was significantly higher(P< 0. 05)than that of normal nude mice (Ct 22. 18), and if there were metastatic lesions that were visible through the naked eye, the expression of Alu (Ct 14. 29) was very significantly higher than that of normal nude mice (P< 0. 01). Conclusions In a model of human gastric cancer metastasis, the expression of the Alu gene positively correlates with the degree of metastasis, namely the higher expression of Alu, the more metastatic tumor cells were present and the more obvious the metastatic foci were in each tissue.