In this article, three-phase asynchronous motor and photoelectric encoder are taken as the research objects. In order to solve the problem of delay in the velocity feedback measurement result of asynchronous motor by photoelectric encoder, this article proposes a velocity feedback observation algorithm which introduces parameters according to different velocity instructions. The proposed method ensures that the speed feedback of asynchronous motor can keep good tracking effect under different speed instructions, reduces feedback delay, and the oscillation of speed tracking waveform is small. Stability analysis is also carried out in this article to ensure the reliability of the system. In the whole control system, the position signal output by the photoelectric encoder is the input of the algorithm, and the output of the algorithm is the speed feedback of the system. The proposed method establishes the speed control system model of three-phase asynchronous motor through MATLAB/Simulink for simulation, and the experiment is carried out based on the simulation. The simulation and experiment are compared with the traditional differential velocity measurement method of encoder. The results show that the velocity observation algorithm proposed is verified under different velocity instructions and varying loads, and the system has smaller steady-state error, better dynamic response, and good robustness.