Abstract: Based on convex combination, a design method for nonlinear PID controller is proposed and its parameters are analyzed. This kind of nonlinear PID controller holds a flexible gain-schedule by selecting its parameters simply. Comparing with the traditional PID controllers, it can give better tradeoffs for some systematic performances which are incompatible. To testify its validity, an industry process with time delay and a drive system with three orders are considered, and the simulation results show its validities.