Abstract: According to the statistics of domestic nuclear power plant CPR1000 units, the common failure modes in the steam generator level control about the master/bypass valve switching process were described. The main modes include that the master/bypass valve switching threshold owes excellent, the master/bypass valve frequently switches and the master valve opens too late. And then a solution was raised about how to improve the master/bypass valve switching process, including switching point optimization, disturbance value control and difference control. This solution is performed in the project site and is verified feasible and effective.