In order to construct the in vitro cell culture model occurring in biochemical and biophysical environment in vivo, and to establish quantitative detection and control of mechanical properties of substrate, a low modulus material polyacrylamide hydro-gel (PAHG) was synthesized and used as the substrate material for in vitro cell culture. Using a modified tensile device based on the principles of buoyancy for balance out gravity deformation and by detecting the minor deformation with the aids of computer graphic processing software, the measurement of low elastic modulus (E) of PAHG was established. By analyzing a large number of experimental data, the effect of two key factors (molar ratio of cross-linker/monomer and water content) on elastic modulus was investigated, and the influence of cross-linker/monomer (d) on saturated water content (w) was also discussed. Mathematical model for d, w and E of water saturated gel in vitro cell culture state was built up by regression analysis of experimental data. Based on the model, the d for PAHG with a given elastic modulus in water saturated state was calculated and applied to the synthesis of PAHG. The results showed that the elastic modulus of thus-obtained PAHG in water saturated state is in agreement with the given value with a relative error of 0.025-0.12, suggesting that the mathematical model is applicable for the prediction of properties of low modulus materials.