The invention discloses a beam optimization method based on a user discovery stage in a millimeter wave system, comprising: modeling a millimeter wave communication system by adopting a random geometric method, and determining a path loss of the millimeter wave communication system and a beamforming gain model to obtain a receiving signal of the millimeter wave communication system; establishing coverage and capacity expressions of the millimeter wave communication system, comparing and analyzing the coverage performance of the system without considering interference and noise; determining therelationship between the capacity of the millimeter wave communication system and the search delay with the beam width as the intermediate quantity, optimizing the beam width to obtain the optimal system performance; using the beamforming technique in the user discovery phase of the millimeter wave to obtain the optimal beam width, and scanning the entire beam space for user search. By optimizingthe scanning beam width of the user discovery phase of the millimeter wave system, the invention solves the problem of the balance between the search delay and the system capacity, and obtains the optimal system performance, thereby saving the cost.