Abstract: The paper introduces the operation state and the facility improvement, including localization of the laddertron and voltage divide resistor, upgrading of the accelerator tube, the injector and radiation interlock system, as well as building of new beamlines during the operation for 20 years of Beijing HI-13 tandem accelerator. In the past 20 years the machine operated for over 80 000 h, provided beam time over 70 000 h and over 30 ion species, and good operation state was kept.