The invention relates to a spiral conveying type septic tank cleaning device and a septic tank cleaning method. The spiral conveying type septic tank cleaning device comprises an outer auger sleeve arranged in the longitudinal direction, the side wall of the upper portion of the outer auger sleeve is communicated with an obliquely-upward output pipeline, and an auger shaft is arranged in the outer auger sleeve and is driven by an electric mechanism to be used for conveying accumulated excrement and mud in a septic tank upwards spirally. The septic tank cleaning method includes the following steps that firstly, the output pipeline is connected with a transfer cart through a conveying pipeline; secondly, the outer auger sleeve is put into the septic tank under the gravity of the spiral conveying type septic tank cleaning device so that mud in the outer auger sleeve can be cut away from the mud in the septic tank; thirdly, the spiral conveying type septic tank cleaning device is held by hand or through a mechanical device, a vertical motor is started so that spiral blades of the auger shaft can push the mud in the outer auger sleeve to move upwards, and then the mud is conveyed to the transfer cart through the output pipeline. The device is compact in structure and capable of removing the accumulated excrement and mud in the septic tank conveniently, and meanwhile the cleaning method is simple and convenient to implement.