Abstract: In case of occurrence of gas overflow during managed pressure drilling, improper handling may lead to further overflow or lost circulation, or even blowout, so in order to solve the above problem, the main factors were analyzed which affected bottom hole pressure stability and well control safety during managed pressure drilling, and presented the calculation formula for maximum allowable gas flow volume during managed pressure drilling and also provides a new method for fluid supplementing and gas bleeding during managed pressure drilling. Numerical simulation and full-size wellbore experiment proves the feasibility of this new method, hence improving the handling method for managed pressure drilling gas flow.