A pulse constant-current source based on capacitor discharge was developed for LIA accelerator. Theoretic analysis and simulation for this source was proceeded. Numerical simulation has consistent result with experiment. The experiment result shows that this kind of source can work in pulse and its input power has reduced greatly. When the output current is 500 A and current duration is 0.3 s, this source has an output current of 0.2%, input power of 400 W and output power of 25 kW. This kind of source is very suitable for LIA.