The invention discloses a two-stage sewage sedimentation purification device and a working method thereof. The two-stage sewage sedimentation purification device comprises a fixed seat, a secondary sedimentation tank, a mixing motor, a controller, a primary sedimentation tank, a primary sedimentation tank liquid indicator, a buffer tank, a water inlet pipe and a water pump, wherein the secondary sedimentation tank and the primary sedimentation tank are arranged in the fixed seat; the primary sedimentation tank liquid indicator is arranged on the inner wall of the primary sedimentation tank; the controller is located on one side of the top of the fixed seat; the mixing motor is located at the center of the top of the secondary sedimentation tank; the buffer tank is located on one side of the primary sedimentation tank, and the water inlet pipe is arranged at one end of the buffer tank and communicated with the buffer tank; the water pump is located between the secondary sedimentation tank and the buffer tank. The two-stage sewage sedimentation purification device is convenient to maintain and mount and high in automation degree, occupies small area and has low manufacture cost.