It is of significant practical value to investigate the strength variation of unsaturated residual soil with different water contents, and establish the computational formulae between them. In the general triaxial instrument, strength tests were conducted on unsaturated residual soil. The results indicated that the shear strength of unsaturated residual soil decreased significantly with the increase of the water content, which demonstrated that water contents had considerable influence on strength. Quantitative analysis of the strain softening characteristics of unsaturated residual soil was done by adopting peakresidual stress ratio. It was found that the optimum water content equaled the critical water content where stressstrain curve was transformed from softening to hardening, the value of c decayed exponentially with the increase of water content, and the value of φ decayed linearly. Based on these results, the integral stress strength formula of unsaturated residual soil was proposed, which can be applied in practice and provide reference in practical situations.