This study aimed to prepare similar materials- gypsum mortar Kaolin similar material(components: quartz sand, Kaolin, gypsum, water and laundry detergent) for weak surrounding rocks which can be conformed to standard, the weak surrounding rocks mass of main mechanical parameters in Class IV tunnel has been chosen as the reference standard, and tests were performed for this similar material to research. The methods orthogonal experiments and range analysis were used to analyze experimental data to obtain mechanical parameters including cohesive strength , internal friction angle and weight, study the various components of gypsum mortar Kaolin similar materials influence on their mechanical parameters, and select the best ratio for Grade IV soft rock;the tests triaxial shear experiments and repeated experiments were used to analyze the mechanical characteristics of similar materials under different confining pressures. The research results indicate that, the water content has the greatest influence on the mechanical parameters cohesion and internal friction angle of similar materials of gypsum mortar Kaolin. When the water content is increased the cohesive force decreases rapidly and the internal friction angle increases slowly; on the other hand ,either increasing Kaolin content or decreasing gypsum content can lead to an obvious increase in cohesive strength and decrease in internal friction angle; then sand content has little effect on the results. In addition while quartz sand turned out to be the most important factor affecting the weight about the mechanical parameters of similar materials, water second, Kaolin and gypsum last.