The invention discloses a power system switching device and method. The device comprises a high speed mechanical switch, power supplies, thyristor valve bodies, a contactor, a load, a current transformer and a voltage transformer. The power supplies, the voltage transformer, the high speed mechanical switch, the thyristor valve bodies, the contactor, the load and the current transformer are connected in sequence. The method comprises the switching between the power supplies in the state that the power supply I and the power supply II are normal, the state that the power supply I breaks down, the state that the power supply I recovers from a fault, the state that the power supply II breaks down, and the state that the power supply II recovers from a fault. According to the power system switching device and method, the valve bodies work only when switching is carried out, and a cooling device needed under the condition that the valve bodies work for a long time is omitted. The number of the groups of valve bodies needed during switching is reduced to one from three of the prior art, the switching performance is not influenced, cost and the floor space are reduced greatly, and the reliability of the device is improved.