Objective To study the effect of immunotherapy on expression of CD14+mHLA-DR and the serum levels of immunoglobulin (IgG, IgA and IgM) in patients with severe pneumonia, so as to discuss the feasibility of immunotherapy for severe pneumonia. Methods From January 2012 to April 2014, 120 cases of patients with severe pneumonia treated in the intensive care unit (ICU) and pneumonia department were collected. Patients were randomly divided into control group (60 cases) and treatment group (60 cases). The control group was administrated with conventional therapy , and the treatment group was given thymosin α1 for immune treatment for 7 days. The mHLA-DR expression and the level of IgG , IgA and IgM of the two groups before and after the treatment were compared. Results After thymosin α1 treatment, mHLA-DR expression rate was elevated , and the serum levels of IgG , IgA and IgM were elevated in the treatment group , and the difference was statistically significant (P < 0.05). While there was no statistically significant difference betweenthe above indicators before and after treatment (P > 0.05). Conclusion After immune treatment with the use of thymosin α1 , immunologic suppression can be prevented , and cellar immune function of severe pneumonia patients can be improved.