Objective To observe the effect of Tanreqing combined with methylprednisolone on children with severe mycoplasma pneumonia（SMPP） and the effect of T lymphocyte subsets. Methods 112 children with SMPP in our hospital were randomly divided into the two groups. The control group（n=56） was treated with methylprednisolone, meanwhile, the observation group（n=56） was additionally administered Tanreqing. The efficacy（each time index）and the safety of the two groups were compared. The T cell subsets before and after treatment were analyzed. Results The effective rate of observation group (94.64%) was significantly different from that of control group (75.0%) (P<0.01). The time of fever reduction（5.24±1.53）d, cough disappearance （6.97±3.26）d, lung rales subside（5.83±1.39）d and lung shadow disappearance（7.93±2.46）d in the observation group were significantly shortened compared with the control group （6.87±2.15）d,（9.79±3.73）d,（7.79±1.46）d,（11.04±4.82）d，with statistically significant difference (P<0.01).The CD3+, CD4+ and CD4+/CD8+ in the two groups were higher than those before treatment, but CD8+ was lower. The indexes of the observation group were （39.21±9.56）%,（34.28±6.43）%,（1.45±0.57）%, and compared with the control group （6.87±2.15）d,（9.79±3.73）d,（7.79±1.46）d,（11.04±4.82）d，the index changes were more prominent, with statistically significant difference (P<0.05). Moreover, there was no difference in adverse reactions in both groups(P>0.05).Conclusion Tanreqing combined with methylprednisolone significantly improves the clinical efficacy of SMPP in children, and effectively improves the cellular immune function of children