In order to solve the problem of high computational complexity of traditional multi-user mmWave relay system beamforming methods, a Singular Value Decomposition (SVD) method based on Deep Learning (DL) was proposed to design hybrid beamforming for the optimization of the transmitter, relay and receiver. Firstly, DL method was used to design the beamforming matrix of transmitter and relay to maximize the achievable spectral efficiency. Then, the beamforming matrix of relay and receiver was designed to maximize the equivalent channel gain. Finally, a Minimum Mean Square Error (MMSE) filter was designed at the receiver to eliminate the inter-user interference. Theoretical analysis and simulation results show that compared with Alternating Maximization (AltMax) and the traditional SVD method, the hybrid beamforming method based on DL reduces the computational complexity by 12.5% and 23.44% respectively in the case of high dimensional channel matrix and many users, and has the spectral efficiency improved by 2.277% and 21.335% respectively with known Channel State Information (CSI), and the spectral efficiency improved by 11.452% and 43.375% respectively with imperfect CSI.