ObjectiveTo study the changes and clinical value of platelet(PLT) parameters and coagulation indicators in children with severe pneumonia. Methods97 children were divided into severe pneumonia group Ⅰ and severe pneumonia group Ⅱ according to whether children were associated with other diseases besides severe pneumonia, and 30 healthy children were in control group. The levels of PLT count, mean platelet volume(MPV), prothrombin time(PT), activated partial thromboplastin time(APTT), fibrinogen(FIB), antithrombinⅢ(ATⅢ), and Ddimer(DD) among three groups were compared. ResultsThe differences of PLT,MPV,DD and ATⅢ activities were all significant  among  three groups (all P<0.05). PLT, MPV and DD levels in group Ⅰwere all significantly higher than those of control group (［454.00±157.00］×109/L vs ［300.00±63.00］×109/L ; ［9.66±1.24］fL vs ［8.90±0.37］ fL; ［0.47±0.37］ mg/L vs ［0.27±0.06］ mg/L, respectively); ATⅢ activity in groupⅠ was lower than control group(［79.91±20.34］% vs［107.03±8.11］%) (both P<0.05). ATⅢ activity and  PLT level in group Ⅱwas (66.11±11.12)% and (279.00±185.00)×109/L  respectively, which were both significantly lower than  group Ⅰ, MPV and DD level was （10.37±1.51）fL and （0.70±0.46） mg/L respectively, which were both higher than groupⅠ (both P<0.05). ConclusionThere is obvious coagulation dysfunction in children with severe pneumonia. The changes in PLT,MPV, ATⅢ and DD levels are associated with the severity of pneumonia.