There exists 100 Hz ripple in the DC side capacitor voltage of the cascaded static var generator（SVG），and the filter circuit is often used in the detection of DC side voltage.Mainly the effect of the filter circuit on the stability of the DC side voltage is studied.The DC side voltage closed-loop control model containing the filter circuit is established according to the principle of the energy balance.An analysis of the stability of the control model shows that the necessary condition for the robust stability of the system is to obtain the regulator integral time constant greater than the filter time constant.A 13-level SVG experimental prototype is built.Experimental results under 220 V and 3 000 V voltage respectively have verified the correctness of the stability analysis.