An all-silicon PIN photodetector based on black silicon microstructure is reported. The device combines the characteristics of broad spectrum and high absorption of black silicon structure and the characteristics of high quantum efficiency and high response speed of PIN photodetectors. By adding a black silicon microstructure layer based on the traditional silicon PIN photodetector structure, the response characteristics of the detector in the near-infrared band are improved without affecting the response speed. A method is proposed to solve the contradiction between quantum efficiency and response speed in the vertical structure of the PIN photodetector. The test results show that the quantum efficiency of the device can reach 80%, and the peak wavelength is 940 nm. The light responsivity reaches 0.55 A/W, and the dark current is about 700 pA. The response time is 200 ns.