The characteristics of PID controller, Active Disturbance Rejection Controller (ADRC) and Linear Active Disturbance Rejection Controller (LADRC) are introduced in the paper, then the parts which can be improved are analyzed, which leads to the topic of balancing linear and nonlinear elements in controller. LADRC with FFTD is used as an example in simulation experiment operated in Matlab7.0.The results shows that the control effect of LADRC with FFTD is better than other three controllers above. The simulation results and perspectives in paper offers reference for combining linear and nonlinear controller and balancing difficulty and performance.