Abstract: Objective　To investigate the change of the platelet function in children with primary immune thrombocytopenia (ITP) before and after treatment. Methods　The platelet indices, immature platelet fraction (IPF%), immature platelet counts (IPC), granule membrane glycoproteins of platelet (CD62p, PAC-1, CD42b) were tested by automatic blood cell analyzer and flow cytometry (FCM) in 18 children with ITP before treatment and after complete response and in 17 children undergoing elective surgery (control gourp). Results　Compared with control group, MPV, PDW, P-LCR and IPF% were significantly higher and PLT, PCT, IPC were significantly lower in children with ITP. The expressions of three platelet membrane glycoproteins (PAC-1, CD62p, CD42b) were significantly lower in children with ITP. After treatment, children with ITP achieved completely response. Compared with before treatment, MPV, PDW, P-LCR and IPF% were significantly lower, and PLT, PCT, IPC, and the expressions of three platelet membrane glycoproteins (PAC-1, CD62p and CD42b) were significantly higher. Conclusions　The platelet function is depressed and in status of low activity in children with ITP. The relative platelet indices provide new references for the diagnosis and the judgment of therapeutic effect in ITP patients.