Abstract: In three-loop autopilot design,if the dynamics of those hardwares such as actuator,gyro,accelerometer,structural filters and so on is considered,the autopilot open-loop crossover frequency should be constrained in order that the system stability requirement can be satisfied.Based on the pole placement method,a nonlinear equation with open-loop crossover frequency constraint is found.Solving this equation,the non-dominate poles will be obtained.Finally,through an autopilot design example,it is demonstrated that this method is very convinced to be used in the three-loop autopilot engineering design.