Normally, the control of a threephase voltage source PWM rectifier (VSR) adopts a cascade PI control strategy composed of outer voltage loop and current internal loop. However, the inaccurate decoupling of inner current loop results in poor rapidity and robustness of DC side voltage for VSR. Therefore, flatnessbased control (FBC), a new nonlinear control method, is employed in the present study to improve the control performance of the inner current loop. Compared with PI control, this method can achieve the feedforward dynamic decoupling of current accurately. In the meanwhile, the FBC control can also improve robustness for parameter changes of the system and external disturbances, and then enhance the dynamic performance of the system significantly. Finally, the correctness and superiority of FBC control are verified by conducting theoretical analysis and simulation tests