Objective: To analyze the changes of coagulation indexes and their predictive value for disease severity in children with mycoplasma pneumoniae pneumonia (MPP). Methods: A total of 120 children with MPP treatedShangrao City People"s Hospital were enrolled between January 2023 and December 2024. According to disease severity, they were divided into MPP group (n=78) and severe MPP (SMPP) group (n=42). The general data of children were collected and analyzed. According to different imaging findings, children with MPP were divided into MPP group (56 cases), MPP+lung consolidation group (26 cases), MPP+lung consolidation+pleural effusion group (20 cases) and MPP+necrotizing pneumonia group (18 cases), and coagulation function indexes in the four groups were compared. The predictive value of coagulation function indexes in MPP combined with necrotizing pneumonia was analyzed by receiver operating characteristic (ROC) curves. Results: There was no significant difference in gender, age or body weight between MPP group and SMPP group at admission (P>0.05). Compared with SMPP group, NE, CRP, incidence of lung consolidation, total duration of fever and total length of hospital stay were lower in MPP group (P<0.05). There was no significant difference in TT, PT or FIB among the four groups (P>0.05), but there were significant differences in D-dimer, FDP and APPT in the four groups (P<0.05). The more severe the disease, the higher the D-dimer and FDP, and the lower the APPT (P<0.05). The results of ROC curves analysis showed that ACU values of D-dimer, FDP and APTT for predicting MPP combined with necrotizing pneumonia were 0.872, 0.765 and 0.817, lower than that of combined detection (0.974, P<0.05). Conclusion: D-dimer and FDP are increased, while APTT is decreased in MPP children. All the above indexes can predict disease severity, and combined detection has higher diagnostic value.