Massive slope engineering exists in large water conservancy projects. The artificial and natural rock slopes are high and steep with diverse lithologies, and the stability and safety of high slopes are the guarantee for the overall project to be effective. This paper presents a parameter inversion procedure for rock slopes based on statistical regression models using monitoring data and coupled analysis of seepage and stress. It is applied to the intake slope of a hydropower station in Southwest China. The results show that based on the strength parameters from inversion, the relative error between the measured and calculated displacement of the monitoring points is less than 4.55% under the water level rise and fall inversion conditions, and less than 4.01% under the validation condition, meeting the requirements for engineering applications. The slope stability safety factor meets the requirements specified in the regulations. The inversion procedure proposed in this paper can provide reference for the determination of high slope strength parameters in this project and other projects.