In order to solve the problem of high complexity and many influencing factors in existing energy-efficiency optimization algorithms in IRS-assisted millimeter wave communication systems, we propose a high energy-efficiency optimization algorithm based on fractional programming theory. Specifically, we used Dinkelbach and successive convex approximation techniques to jointly optimize the hybrid precoding at the base station and the phase shift matrix of IRS. The simulation results show that, compared with the traditional system without intelligent reflecting surface, the energy efficiency of the system under the joint design of hybrid precoding and phase shift matrix is improved by about 215%. The results also show that deploying more low-cost passive elements on reflecting surface can significantly improve the downlink energy efficiency of the system.