In order to improve the efficiency of permanent magnet brushless D.C. motor (BLDCM) driving air compressor, genetic algorithm embed BLDCM module which optimizes the air compressor was put forward. Optimized target of genetic algorithm is the efficiency of BLDCM. Optimized variables are the diameter of low pressure cylinder, the diameter of high pressure cylinder, the journey of low pressure piston, the journey of high pressure piston and the rotate speed of BLDCM. The values of variables were passed to BLDCM module by sim function. Simulation time was controlled by sim function. The efficiency value was passed to genetic algorithm program. Simulated result shows that the efficiency of BLDCM is higher than that before optimized. The experimental result shows that the specific power of air compressor is almost the same as that before optimized at 0.7MPa, but is much less than that before optimized at 2.5MPa. The result also shows that genetic algorithm embed BLDCM module which optimized the air compressor is available and practical. 