Objective To investigate the effect of Mycoplasma pneumoniae (MP) infection on the function of T lymphocytes in the bronchoalveolar lavage fluid (BALF) of asthmatic children in acute and stable periods and the relationship between MP infection and asthma. Methods Seventy-one hospitalized children (with bronchitis, pneumonia, and asthma) were divided into non-MP infection control group (group A, pneumonia and bronchitis without MP infection), non-MP infection asthma group (group B), and MP infection asthma group (group C). Flow cytometry was used to determine CD3⁺, CD4⁺, and CD8⁺ T cell counts and CD4⁺/CD8⁺ ratio in BALF among all children in acute and stable periods. Results Compared with group A, groups B and C showed significant differences in CD3⁺, CD4⁺, and CD8⁺ T cell counts and CD4⁺/CD8⁺ ratio (P<0.05) in acute and stable periods, had decreased CD3⁺ and CD4⁺ T cell counts, an increased CD8⁺ T cell count, and a significantly decreased CD4⁺/CD8⁺ ratio (P<0.05) in the acute period, and had decreased CD3⁺ and CD4⁺ T cell counts and CD4⁺/CD8⁺ ratio and an increased CD8⁺ T cell count (P<0.05) in the stable period. Compared with group B, group C had significantly decreased CD3⁺ and CD4⁺ T cell counts and CD4⁺/CD8⁺ ratio (P<0.05) and a significantly increased CD8⁺ T cell count (P<0.05) in the acute period and showed no significant differences in CD3⁺, CD4⁺, and CD8⁺ T cell counts (P>0.05) and a significant decrease in CD4⁺/CD8⁺ ratio (P<0.05) in the stable period. Conclusions The immunological function of T lymphocytes in the airway declines significantly among asthmatic children with MP infection in acute and stable periods, leading to immue system disorder. MP may be associated with the pathogenesis of asthma.