In order to accurately estimate the rotor angle and speed for sensorless control of interior permanent magnet synchronous motor (IPMSM), a nonlinear state observer was presented based on motor state equations and nonlinear theory, and the stable criteria of the observer was stated based on Lyapunov stable theory. Considering the influence of load disturbance, the load torque estimation was added to the observer. Because the modeling and sampling were not perfect, errors existed between the real states and the estimated states, so a compensation method was introduced. The convergence and accuracy of the state observer were proved through simulations and experiments.