As an effective means for the exploitation of Hot Dry Rock (HDR) resources, the Enhanced Geothermal System (EGS) has broad development prospects and a great utilization value. Therefore, it is particularly important to predict its capacity and longevity. In order to realize the productivity and longevity prediction of the double-well EGS, the productivity and longevity prediction methods of the EGS system under different working conditions were analyzed through theoretical derivation and numerical simulation. Firstly, based on the Dupuit formula and the endothermic formula, the EGS productivity and longevity control equation was established to provide theoretical support for EGS longevity prediction. Then, according to the groundwater flow equation and the heat transfer equation, combined with the Newton’s cooling law, five factors affecting the four unknown parameters in the EGS productivity and longevity control equation were analyzed. The four unknown parameters were the reduction of thermal reserves, the amount of geothermal compensation, the average conversion temperature of production wells, and the shape coefficient of thermal reserves. The five factors obtained were the initial temperature of thermal storage, the injection temperature of thermal medium, the volume of thermal storage, the specific surface area of thermal storage, and the EGS running time. Under the condition of considering the geothermal compensation, the three parameters of EGS with double-well were used to analyze, correct and quantify the influence factors of each unknown parameter when the thermal storage breakthrough occurred, and then obtained the prediction formula of the four unknown parameters changing with the five factors. Based on the above results, a method for predicting the productivity and longevity of the double-well EGS was obtained: using the EGS productivity and life control equation, the prediction formula of four unknown parameters, and the thermal reserve permeability to predict the productivity and longevity of the double-well EGS. Finally, the prediction method of production capacity and longevity of the double-well EGS was used to predict the working conditions of the existing literature and compare them. The two results were in good agreement, which proved the applicability of the control equation and the prediction formula and the accuracy of the prediction method.