In　the　measurement　of　nonlinear　power　capacitor,　large　DC　(direct　current)　voltage　and　small　AC　(alternate　current)　sinusoidal　voltage　connected　in　series　are　applied　to　the　nonlinear　capacitor.　In　this　situation,　measurement　precision　of　the　capacitor　AC　sinusoidal　voltage　and　current　are　critical　to　the　accurate　calculation　of　nonlinear　capacitance　parameter.　Owing　to　the　voltage　level　diversity,　voltage　regulation　circuit　is　needed　between　the　measurement　terminals　and　measurement　instrument.　Though　deliberately　designed,　measurement　circuit　introduced　amplitude　and　phase　error　is　inevitable.　In　this　paper,　an　accurate　AC　sinusoidal　small　signal　measurement　method　is　proposed　to　promote　the　measurement　precision.　The　small　signal　model　of　the　voltage　regulation　circuit　is　deduced　first.　The　amplitude　and　phase　angle　of　the　measured　sinusoidal　small　signal　is　calculated　by　software　phase　lock　loop　(SPLL)　method,　after　which　the　amplitude　and　phase　angle　error　is　compensated　based　on　the　deduced　small　signal　model　of　the　voltage　regulation　and　filter　measuring　circuit　and　frequency　response　method.　The　correctness　and　effectiveness　of　the　proposed　accurate　AC　sinusoidal　small　signal　measurement　method　has　been　verified　by　simulation　experiment.　©　2024　SPIE.