Abstract: It is important to study the effect of water content and reinforcement rate on the strength of rice straw-reinforced soil, which has an important effect on promoting the application of rice straw-reinforced soil in slope ecological protection. The moisture content of the six kinds of reinforcement ratios (0 to 0.5%) was changed by adding water and with the drying method, and the indoor direct shear tests were carried out. The result shows that (1) the shearing strength, cohesive force and internal friction angle of the reinforced soil samples, which are obtained by the adding water method, increase first and then decrease with the increasing water content under different rates of reinforcement. When the water content is 14.8%, their peak values appear. The shearing strength, cohesive force and internal friction angle of the reinforced soil samples, which are obtained by the drying method, decrease gradually with the increasing water content. (2) The shear strength, cohesive force and friction angle, which are obtained by adding water and with drying method, all have a critical value of moisture content, which is about 19%. (3) Under the same growth rate, the effect of moisture contents on the shear strength of the reinforced soil is greater than the reinforcement ratio.