Objective The functional status of the host immune system plays an important role in viral infection．The aim of this work was to study the differences among four immunodeficiency strains of mice and two wide-type mouse strains after infection of influenza A ( H1N1) ( A /California /7 /2009 ( CA7) ) virus ． Methods The six inbred laboratory strains of mice were anesthetized by inhalation of ether and inoculated intranasally with 0. 05 mL of infectious virus H1N1 ( CA7) suspension． The body weight loss kinetics，survival rates and pathological changes in the lung tissue after infection were examined． Results BALB / c mice and four immunodeficiency strains of mice showed high susceptibility in the viral infection compared with C57BL /6 mice． Half of C57BL /6 mice survived，while the mortality rates of the remaining five strains were 100% ． C57BL /6 mice exhibited diffuse interstitial pneumonia in the initial stages of infection，and the lesions were gradually restricted to the late stage． BALB / c mice and four immunodeficiency strains of mice showed severe diffuse interstitial pneumonia，bronchial epithelial degeneration and necrosis，and there were significantly less inflammatory cells than that in the C57BL /6 mice． Conclusions Innate immunity and adaptive immunity play a major role at the early and late stages of the infection of influenza A ( H1N1) virus． The state of the host immune system affects the infection and prognosis of influenza A ( H1N1) virus infection．