The moisture content of filling has a major impact on the soil shear strength parameters, which thereby affects the calculation of earth pressure and then influences the stability of the retaining walls. This article studies on the basis of the previous studies, which is about the influence of the moisture content to shear strength parameters of the unsaturated filling. By having shear tests of soil samples with ZJ type direct shear apparatus and combining with relevant knowledge of the strength theory, shear strength parameters C and φ are obtained. Then the experimental results are given numerical simulations to determine the influence coefficients of the affect of moisture content to C and φ, and are used to get the relation formulas of moisture-cohesion, moisture content-internal friction angle with good goodness of fit.When soil samples are given the pressure experiments by using universal testing machine,the soil particle size distribution and the density of filling are basically consistent, and only change the moisture content of filling to study the influence of fillings of different moisture contents to the performance of retaining walls. In the experiments, it can be found that with the pressure increasing, the compressibility and the moisture content of the filling show a nonlinear relationship. At first the compressibility increases with the increases of moisture content , and then decreases when the moisture content reaches a certain value. By the end of the experimn, according to Rankine's earth pressure theory , the earth pressures of retaining walls are calculated corresponding to a variety of filling state, and the relation formulas of the moisture content-active earth pressure, moisture content-passive earth pressure are getting by the use of numerical simulations to the results.