A mathematical model of grid voltage and power is established in ab coordinate system for single-phase PWM rectifier. According to the differential flatness theory, the state variables, outputs and intermediate variables of the control system are chosen, presenting that the differential flatness based direct power control for single-phase PWM rectifier. The controller consists of feed-forward control and nonlinear error feedback compensation. Feed-forward control plans control state variables’ reference trajectories according to the desired outputs and nonlinear error feedback compensation adjusts flat outputs of control system to eliminate errors between desired and actual outputs. Simulation results show that the DC voltage can keep a good stability as its grid voltage amplitude and phase change and follow the active and reactive power’s reference trajectories to make a rapid power response. The system has strong anti-interference ability and good robustness.