The comparative study of optimized switched flux permanent magnet machine (SFPMM) with different load conditions and constrains was presented. By taken a 6/8 SFPMM as example, the sensitivity of parameters was investigated to decide the optimized sequence. With the different constrains, such as lightload、rated、overload conditions, the 6/8 SFPMM was optimized at fixed copper loss、fixed current、fixed current density. By comparing the torque density, PM volume, losses and efficiency of the optimized designs, the effective constraint to optimize the SFPMM will be obtained.