The inverter nonlinearity, flux spatial harmonics and detection errors give rise to DC offset and harmonics in the back Electromotive Force（EMF） obtained by the sliding mode observer（SMO），which results in harmonic ripple in the position estimates. This paper proposes a fifth-order generalized integrator（FOGI） based rotor position observer to solve the above problems. On the premise of frequency-locked loop（FLL） to ensure frequency adaptation, the FOGI helps to complete the accurate decoupling and improve the control performance of the Interior Permanent Magnet Synchronous Motor（IPMSM） position sensorless drive system. Under the action of the FOGI, the DC components and harmonics of the EMF estimates are more completely filtered.Thereby, the accuracy of rotor position calculated by the Phase-Locked Loop（PLL） can be improved. In this paper, the FOGI is compared with the fifth-order standard integral equation in the classic control system, and its parameter tuning process is fully and reasonably simplified, simultaneously,when the rapid convergence of rotor position estimation system is guaranteed. Finally, after comparing the performance of dynamic response and interference suppression with the traditional second-order generalized integrator（SOGI），the advantages and effectiveness of control strategy are demonstrated through simulation and 1.5 kW dsPACE semi-physical experiments.