STATCOM can be used as both dynamic reactive power compensation device and active power filter to improve the power quality of a power grid. This paper describes the active filter function implemented into an existing STATCOM control. The paper explains firstly the filtering control system of the STATCOM, starting from the introduction of active power filter principle, harmonic current detection and tracking control. After that, the parameter design, open-loop characterization and simulation verification of the proposed filtering control scheme are carried out. The PSCAD simulation results show that the active filtering control scheme proposed in this paper can effectively reduce the harmonic content in the system and has good stability.