In the construction of water conservancy and hydropower projects, prestressed anchor cables (rods) are usually used to strengthen unstable slopes to improve their stability. However, up to now, the design of prestressed anchorage is mostly too conservative, resulting in too much engineering waste, and the anchorage design theory and method need to be further studied. By analyzing the factors affecting the design parameters of rock anchor and applying optimization and decision theory, the method of determining the design parameters of rock anchor is proposed, and the decision support system RSASYS for rock anchor support design is established, which provides a new analysis method for engineering designers to design rock anchor. The practice proves that this method is feasible and can obtain great economic benefit.