The permanent magnet flux identification system of permanent magnet synchronous motor based on MRAS under the condition of speed sensorless control was studied. Only the speed and permanent magnetic flux were estimated. It satisfies a identification model of full rank and avoids the problem of different initial values different identification values. The convergence and uniqueness of parameter estimation were also ensured. The essence of the rank deficient problem and deduct the identification adaptive law of speed and permanent magnet flux respectively were analyzied. The simulation results showed that the control system could accurately track the speed of the rotor under the speed and load transient change, and had good robustness, with reduced sensitivity on the parameters.