According to commutation process of inverter, the mechanism of commutation failure is analyzed. Two methods to distinguish commutation failure in HVDC transmission system are compared, which are minimum extinction angle distinguishing and minimum extinction area distinguishing. A minimum extinction area control strategy is presented to improve ability of suppressing commutation failure in inverter station. Taking Lingfeng DC project as research object, a control and protection model based on PSCAD/EMTDC is built, and control experiment with minimum extinction angle control strategy and extinction area control strategy is done. The simulation results show that minimum extinction area control strategy is more effective than minimum extinction angle control strategy in suppressing commutation failure, and commutation failure can not be avoided if AC voltage dropped seriously.