3.6 MW (66 kV/55 A) high voltage power supply system was developed for the 170 GHz ECH&CD system in KSTAR. It consists of the cathode power supply (CPS), anode power supply (APS), and body power supply (BPS). Currently, modulation frequency of APS was limited to less than 1 kHz due to the parasitic capacitance of Zener diode circuit including gyrotron. In order to solve these lacks of controllability and high frequency modulation of APS, the existing APS is replaced by a new type of APS and it is tested for KSTAR 170 GHz gyrotron system. This paper presents the new APS design and characteristics and the test results for 170GHz gyrotron in KSTAR ECH system.