Abstract: NDZ 20 Medical linear accelerator is a kind of travelling wave feedback mo-del. Its energy can be adjusted by changing frequency, phase, output rf-power ofmagnetron and beam loading. It has seven electron energy ranges between 5 to 20MeV and two energy ranges of x-ray (10 MV and 15 MV). Some advanced tech-niques such as AFC, ARC and ADC are used automatically to stabilize controlsystem for frequency, does rate and flatteness of field. Some major componentshave advanced parameter. The machine has run for two years. The ratio of downtime was 2.14% in 1986 and 3.53% in 1987. All parameters have reached or surp-assed the GBW 4-81 stipulated by the National Standards. In the last two years1366 patients have been treated, the clinical cure effect was notable.