Abstract: The structure and characteristic of an injector system of a NDZ-20 medicalelectron linear accelerator are described. A bombarded type of Pierce electron gunis used. There are pre-focusing coil, deflecting coil, steering coil and beam pulselead cutting coil in drift tube region. They control electron beam efficiently forARC, ADC and BLC of the accelerator. ARC and ADC can increace stability andreliability of accelerator operation, and BLC improve energy spectrum of the backfeed accclerator.