The study start on January 18, 2017. The Severe(FⅧ<1%) and moderate hemophilia A (FⅧ1%～5%)children with high titer inhibitor(historical peak inhibitor titer≥5BU ) combining with poor ITI risk(s) were enrolled. The low-dose ITI was alone or combined with immunosuppression.

Poor risk(s) includes:①peak historical inhibitor titer≥200BU ②inhibitor titer≥10BU before ITI initiation ③peak inhibitor titer during ITI≥200BU ④time to titer decline to<10BU before ITI≥24 months ⑤age≥8 years at start of ITI ⑥ITI initiated ≥5 years after inhibitor diagnosis ⑦interruptions in ITI≥2 weeks in duration. The low-dose ITI strategy consist of FⅧ（25-50IU/kg）alone or combining with immunosuppression: prednisone and Rituximab when the inhibitor titer ≥40BU ml/ml before or during ITI.

Inclusion Criteria:

• Males
• from 1 to 14 years old
• severe or moderate hemophilia A;
• inhibitors positive before ITI started.

Exclusion Criteria:

• Females
• <1 or >14 years old
• hemophilia B or mild haemophilia A;
• inhibitor negative before ITI started.