To achieve the laboratory performance test to laser communication system terminal, an optical method to simulate the laser transmission in different distances is required to use in the laboratory. In this paper, the primary design index of a link attenuation system is extracted according to the parameters of the front Fourier- transform lens. This paper cleverly makes use of the thoughts of optical enlargement and cascaded zoom system according to the index. The simulation to space links with variable distances is realized. A simulator system which can realize 3~10 times continuous zooming of a single-stage is designed, optimized by using ZEMAX, and the zoom curve of a single- stage is drawn. The structure of single- stage system with length of 309 mm is compact. The wavefront aberration of the whole field is better than 0.05 λ . The energy of light is concentrated. Through theoretical analysis, four cascaded design can achieve equivalent transmission distance of 103~105 km, so as to satisfy the detection requirements for most of the laser communication terminals.