Abstract: The lumped constant magnetic circuit method is used to analyze and compare the air gap magnetic field distribution of typical single and double-layer rotor structures. Based on this analysis, an IPMSM with I2V type is proposed to further improve sine degree of no-load air gap flux density waveform, achieving high efficiency, high torque density and low iron loss. The V type, IV type and I2V type are selected as the comparative objects for optimization research, the established 2D parameterized finite element analysis（FEA） models are used to optimize and analyze the rotor structures. Under the constraint of same volume of permanent magnets, the optimization models of rotor structures are determined ultimately. The no-load air gap flux density waveforms and harmonic contents of three different rotor structures are analyzed and compared, the results show that no-load air-gap flux density of I2V type have the lowest THD rates. The reluctance torque and average output torque with different current angles are analyzed and compared, the results show that average torque and reluctance torque of I2V type are larger than that of the other two as the amount of permanent magnet is slightly reduced, especially in deep flux weakening conditions, the advantage of reluctance torque is more obvious compared to the other two. The iron loss of IPMSM with different optimized rotor structures are analyzed and compared. Compared with the other two, the results show that the iron loss of I2V type is the smallest. The iron loss of I2V type is significantly less than that of the other two especially under the condition of deep flux weakening conditions. The I2V prototype is processed and manufactured, and a prototype experimental platform is built. Experimental verifications are conducted on the torque, loss, efficiency. The test results are basically consistent with the FEA results, proving the superior performance of the I2V type with three-layer rotor topology proposed in this paper, as well as the correctness of the analysis method and the effectiveness of simulation calculations.