[en] Electron Linear accelerators have varied application for medical and industrial purpose. Medical accelerators at X-band frequency has garnered lot of attention for the reduced size of the beams and the possibility to easily have 'self-shielded machines', minimizing stray radiation and leakages in treatment rooms. At APPD, BARC, development of X-band (9300 MHz), 6 MeV electron accelerators is in process for compact X-ray source for cancer therapy. The electron accelerator will have a 20 keV, 300 mA electron gun which will focus the electron beam to a small radius. In this paper, the design simulation of the electron gun which has been carried out using CST particle studio will be presented. (author)