The invention discloses a method and a system for synchronous sampling of power signals. The method comprises the following steps of measuring the fundamental wave frequency of the power signals; obtaining a product of the preset fundamental wave frequency integral multiple rate and the fundamental wave frequency as the synchronous sampling frequency; according to the principle that the asynchronous sampling frequency is much greater than the synchronous sampling frequency, obtaining the asynchronous sampling frequency which is greater than the synchronous sampling frequency, and obtaining the frequency ratio of the asynchronous sampling frequency and the synchronous sampling frequency; according to the asynchronous sampling frequency, performing high-density asynchronous data sampling on the power signal to obtain an asynchronous data sequence; according to the preset conversion rule, converting any two adjacent asynchronous discrete data points of the asynchronous data sequence and the frequency ratio into a synchronous discrete data point, and generating a synchronous data sequence. The method and the system have the advantages that the synchronous sampling operation is reduced, the synchronous sampling efficiency is improved, and the synchronous sampling frequency is reduced.