A PMSM sensorless vector control system and method is provided. The system includes a Clark transform module, a Park transform module, a Park inverse transform module, a pulse width modulation module,an inverter module, a sliding mode observer, a first comparator, a second comparator, a third comparator, a speed regulator and a current regulator. A sliding mode observer is used to replace a traditional mechanical sensor to detect the position and speed of a PMSM, the cost and size of PMSM control system are reduced, A new type of second-order sliding mode observer is designed by using Lyapunov function method. The second-order sliding mode observer eliminates the chattering of the system without low-pass filter, and obtains smooth back electromotive force signal for rotor position and speed estimation, which improves the observation accuracy and system robustness.