AC filter bank plays an important role in improving safe and stable operation ability of HV/UHVDC transmission. The HV capacitor in filter bank mainly consists of multiple capacitors in series and paral-lel connection. The capacitance of four bridge arm of HV capacitors is not in balance because the actual ca-pacitance of each capacitor

compared to its rated value

has a definite deviation

thus the performance ofthe filter is affected. In this paper

the equilibrium arrangement optimization model of capacitor is set up inaccordance with the actual capacitance of each capacitor in the HV capacitors during the maintenance andalso with the minimum unbalance degree of four bridge arm’s capacitance is optimization target. The solu-tion of the model is performed by the use of improved PSO algorithm so to obtain equilibrium arrangementplan of capacitor. The correctness and practicability of the method is simulated and verified by Matlab

which has reference value in improving filter performance and reactive power compensation ability of filterbank of HVDC transmission system.