The invention provides an alternating current testing device for a Seebeck coefficient. The alternating current testing device comprises a sample table, a chuck, a main heater, an auxiliary heater, amain probe, an auxiliary probe, a main temperature measuring element and an auxiliary temperature measuring element. The main heater, the main probe and the main temperature measuring element are mounted on the sample table; the auxiliary heater, the auxiliary probe and the auxiliary temperature measuring element are installed on the chuck, a temperature controller connected with the main heater and the main temperature measuring element, a lock-in amplifier connected with the auxiliary temperature measuring element, an alternating current power meter connected with the auxiliary heater are connected with a computer separately, and the sample table and the chuck clamp a sample to measure the Seebeck coefficient. The structure is simple. The invention further discloses an alternating current testing method of the Seebeck coefficient. the amplitude delta V of alternating current voltage and the amplitude delta T of temperature oscillation are measured in an input and output alternating current signal mode, the Seebeck coefficient is obtained through calculation according to the ratio of the amplitude delta V of the alternating current voltage and the amplitude delta T of the temperature oscillation, the temperature control requirement is low, the testing speed is high, and direct current signal interference is avoided.