Abstract: Recently, great attention has been paid to short electron pulses because of the requirement for free electron laser(FEL) projects. To generate a 0.2 nC, 5 ps, 2 MeV electron bunch with a normalized emittance better than 50 mm·mrad without compensation coil, a self-bunching RF gun with independently tunable cells (ITC) is employed, which consists of two independent cavities to compress short pulses. The first cell compresses the beam from a high-voltage DC gun and the second is an acceleration cell. The two cells can be power fed independently, and beams with excellent characteristics can be obtained by choosing appropriate feeding power and phase for the two cells. This paper describes the design of an external injecting ITC RF gun (DC-ITC-RF gun) and presents simulation results of beam p