To improve the precision of estimated rotor angle for the interior permanent magnet synchronous motor(IPMSM),this paper presents a novel model based on the linear flux.The rotor position and speed is estimated by the sliding mode observer(SMO) via the current error between the actual current and the estimated current.The effect of stator resistor and inductance on the estimated rotor angle is analyzed quantitatively,and to reduce the effect,Lyapunov function is established to identify stator resistor and inductance.The experimental result shows the validity and reliability of this algorithm.