The objective of the present study is to tackle problems in the simulation of rock body material and the measurement of relative displacement of structural planes in geomechanical model test. Firstly, the deformation characteristics of different rock body materials was simulated, and the composition and preparation method of rock body model material were determined. It was found that the cement, paraffin and engine oil were main factors controlling the deformation characteristics of model materials of high, medium and low performances. Refined simulation using small blocks of different sizes was proposed for the rock materials with various deformation moduli. Moreover, strain test technique was employed to develop a measurement instrument for the relative displacement of structural planes. In the test, the strain changes of measurement points under different loading conditions were recorded by strain gauges, and the displacement process  was obtained according to the calibrating coefficients of displacement and strain obtained before the embedment. The research findings were applied to Xiaowan arch dam model test and the results indicates that both the model material prepared in this study and the measurement technique for relative displacement of structural plane meet the requirements of model test.