The stability of high steep rock slopes directly influences the success or failure of whole engineering construction processes. Slope excavation and reinforcement with prestressed anchor cable can effectively improve the stability of the slope. However, the blasting stress waves have a great impact on the anchor cables that have been installed or are under construction. In this paper, a new simulating method of prestressed anchor cables is proposed for high steep rock slopes in consideration of the construction process and the reinforcement mechanism. And a simple simulating method of slope blasting excavation load is developed. The bearing capacity of prestressed anchor cables under slope blasting excavation is analysed via an ideal generalized slope model based on the left bank slope of the Jinping I hydropower station. The results show that the degree by which the distance from the blasting zone, the damping ratio, the maximum single-shot dose and the grade of the prestressed anchor cable impact the bearing capacity behaviours of the prestressed anchor cable decrease over time. Anchor cables are most prone to vibration failure within 5 m from the outer anchor head. The increase in tensile force is the largest on the anchor head at the slope surface. The impact of the maximum single-shot dose and damping ratio on the small-tonnage anchor cable is greater than that on the large-tonnage anchor cable. The anti-explosion performance of the large-tonnage anchor cable is better than that of the small-tonnage anchor cable. The foundations and experience needed to optimize the parameters of blasting excavation and anchor cable design for similar high-slope projects in China or other regions are presented.