The premise of realizing the vector-control of permanent magnet synchronous generator (PMSG) lies in obtaining the accurate information about angular speed and rotor position. This document puts forward to a novel sensorless control of PMSG based on sliding mode observer and software phase locked-loop (SPLL) which estimates the internal voltage in the rotor-oriented dq-reference frame by using sliding mode observer. SPPL uses the internal voltage estimated to estimate angular speed and rotor position. Under the condition there is much difference between model parameter and actual parameter, the result of simulation of PMSG of directly driven wind turbine used the method indicates that it is robust to parameter variation and exterior interfere, and can accurately estimate rotate speed and rotor position.