The excimer laser as the main light source of photolithographic device, whose energy distribution is required as homogeneous as possible. In order to improve the uniformity of its output energy density, this paper describes a novel trapezoid prism homogenizer. The working principle and the design requirement of the novel trapezoid prism are analyzed in theory. The optimal position of uniform section is calculated, and compared with the normal prism homogenizer. According to the theory that the beam energy refracted by the trapezoid prism is divided into 3 parts then overlapped in the base of the middle high energy, it realizes the use of association with the normal prism in two-dimensional. By means of adjusting the distance from homogenizer to receive screen, the optimal position of uniform section is determined which agreed with the theoretical calculation. Using this novel homogenizer ,the fluctuation of beam uniformity of XeCl excimer laser is less than 4%, it is better than that obtained by using a normal prism homogenizer.