In order to seek a more optimal control system, this study built a DC-DC buck converter and conducted the system modelling according to its parameters, based on which three controllers were designed, including a state-space controller with non-overshooting and non-undershooting(NOUS)algorithm, a NOUS controller with observer and a proportional-integral-derivative(PID)controller. The step responses and transient responses of the converter with 3 different control systems when load changes were shown by an oscilloscope, so that their control performances could be compared. The results indicate that the state-space controller based on NOUS algorithm has better transient response and control precision, while PID controller has advantage in robustness. NOUS controller with observer preserves the advantage of fast convergence, but will lead to amplifying the errors in the system modelling and cause worse control results.