To meet the real-time simulation of ballistic target radar echo precision requirement is a stronger comprehensive project, it is a key to the target detection and recognition. In this paper, a calculation formula of a large ballistic target in explicit RCS arbitrary angle of sight is given under microwave frequency based on GTD and PO method. The results computed by using this method agree with that by using the FEKO software and the calculation speed is extremely high. Using the data obtained by this method to realize the High Resolution Range Profiles (HRRPs), the results of simulation and theory are in good agreement with each other, and can meet the need of real time simulation precision of radar based on reentry ballistic target echo signal of target electromagnetic scattering characteristics.