Abstract: Modeling algorithm based on string-coding clone selection is put forward. In the algorithm, evolution and choice of function structure, arithmetic relation and parameters are completed in elementary function space with string-coding clone selection, therefore, automatic production of forecasting model structures and adaptive determination of forecasting model parameters are realized. Design of string-coding makes it possible to randomly produce an expression in elementary function space; clone selection strategy achieves evolutionary training of string-coding antibodies. Moreover, by design of clone operator to string-coding antibodies, different antibodies evolve coordinately, diversity of antibodies restrains ``precocity'' in evolution. Reliability forecasting model of the weapon system is built uisng the algorithm. Results of experiments show that the forecasting model is of high accuracy, and lays a foundation of reliability forecasting, fault forecasting and maintenance for the control system.