Abstract: In order to measure the noise of the ac filter capacitor accurately and reduce the requirement of the test power source and other equipment in the condition of accurately measurement. This paper is based on the noise test of filter capacitor in Changji –Guquan ±1100kV HVDC project, Based on the bridge circuit injected three different kind of current condition on three different filter capacitor. The three different kind of current condition are these: Full harmonic currents, the former three main harmonic currents and the 70% full harmonic currents of Changji –Guquan ±1100kV HVDC project. The test date show the sound press level and the sound power level are quite near on full harmonic currents inject condition and he former three main harmonic currents inject condition, the maximum difference is 0.4dB.Compare the sound level of full harmonic currents inject condition with the date calculated by the 70% full harmonic currents inject condition, the correctness of the formula is verified. Can use the former three main harmonic currents condition to do the noise test or lower the full harmonic currents ratio to do the test and use the formula calculate the sound power of the filter capacitor.