Aiming at the requirement of AC signal sampling for a disconnect switch controller, a complete solution of software synchronous AC signal sampling was proposed, and the conditioning circuit and the signal acquisition software module of AC signal were designed on the basis of analyzing the feasibility of using sample sequencer to realize simultaneous sampling of AC signals. The sampling task of PQIU electrical parameters of three-phase four-wire AC lines was realized by the built-in ADC system of LM3S9D92, and the performance-price ratio of controller products is improved effectively. The test results show that the precision of AC signal sampling part meets the requirement of technical specification.