In order to evaluate and optimize the seismic performance of ±800 kV UHVDC filter capacitor, a elaborate nolinear finite element model(FEM) is established and the seismic responses of filter capacitor is obtained from time history computing method. Aiming at a ±800 kV UHVDC filter capacitor, it is found that UHV filter capacitor has strong non-linearity and low frequencies and it generates large displacement responses under earthquakes. In addition, the safety factor of hanger insulators for fortification earthquakes doesn’t meet the requirements of relevant codes. Through the analysis on the coefficients of the pretension force and installation angles of bottom insulators. It is concluded that the displacement responses can be reduced by increasing the pretension force in insulators and the maximum axial force of filter capacitor can be adjusted by optimizing the installation angles of bottom insulators, the DC filter can meet the seismic requirements when the installation angle is set as 80 °, the pretension force is set as 40 kN after the specified tension load for hanger insulators is no less than 536 kN.