Objective To investigate the role of D-dimer (DD),procalcitonin (PCT) and C-reactive protein (CRP) levels in diagnosis and prognosis in children with mycoplasma pneumonia (MP) combined with pleural effusion. Methods The clinical data of 58 children with MP combined with pleural effusion were collected.The general characteristics of patients were analyzed retrospectively.The levels of DD,PCT and CRP among onset period group,recovery period group and healthy control group were detected.The levels of DD,PCT,CRP and conventional detection index of pleural effusion among different groups of pleural effusion quantity were detected,and the correlation between increased levels of DD,PCT and CRP and prognosis were analyzed. Results The levels of DD,PCT and CRP of onset period group were higher than those of the recovery period group and control group,and the differences were statistically significant (P<0.01);The levels of DD in recovery period group was higher than in control group (P<0.01).PCT levels had no significant difference between recovery period group and control group (P> 0.05),and the increased levels of CRP in recovery period group was insignificant compared to control group (P=0.015);The proportion of elevated levels of DD,PCT and CRP in onset period group were significantly higher than those of recovery period group;The levels of DD,PCT,CRP,TP,LDH,ADA and WBC with children in large volume pleural effusion were significantly higher than those in small amount pleural effusion and middle volume pleural effusion group,and the level of CRP was positively correlated with DD and PCT in recovery period group. Conclusion The increased levels of DD,PCT and CRP may reflect the severity and prognosis of mycoplasma pneumonia combined with pleural effusion.