The refrigeration requirements are still the main restrictions in the application of mid-wave infrared detector.In this work,a hetero-pin structure InSb Avalanche Photodiode was designed.The GaSb and InP with wide bandgap and lower recombination rate were used to form the heterojunction,and the I region was designed as a separated absorption and multiplication layer.The diffusion current was effectively suppressed by heterostructure,and the JAuger was obviously inhibited at the level of 1×10 -7 A/cm2 at 300K.The main limitation of device was the SRH recombination and band to band tunneling.For optimizing the performance,the dark current mechanism was discussed and the lower impurity concentration was proved to be beneficial for the avalanche process.At 300K,the absorption peak was about 5.1μmwith a responsivity of 2.16 A/W,the optimized gain was 5.7 and the specific detectivity was 2.866×109cm·Hz 1/2·W -1.