The use of compulsators as a compact power supply has the potential to he used in elecltrogun applications. Although compulsators have been developed for electromagnetic railguns for some years, the use of compulsators in the power supply of electrothermal-chemical guns (ETCGs) may give rise to problems such as providing the proper current waveforms and matching of the capillary load. Of particular importance is the nonlinear characteristic resistance of the capillary load. This paper reports on a staged power supply system based on a compulsator for ETCG applications and describes the working process of the simulative system. The whole system is composed of a compulsator, a high-voltage capacitor, a, capillary, a high-current thyristor switch, a power diode, and a control unit. The high-voltage capacitor is used for igniting the capillary arc, and helps to reduce the output voltage of the compulsator. Models of a compulsator and a capillary are considered as a whole to simulate the system performance. These models can be used to explain the discharge process of the capillary and provide the theory for the parameter choices and the power supply design. Experiments demonstrate that the staged power supply can meet the current and voltage requirements of ETCG applications.