The invention discloses a backpack portable multipurpose water pump and a using method thereof. The water pump comprises a pump shell body, a water storage tank and a water outlet pipe which are arranged on the pump shell body, a pump cover which is connected with the pump shell body, a water inlet pipe mouth which is formed in the pump cover, a water inlet absorption seal device which is connected with the water inlet pipe mouth, and a power shaft, bearings, seal rings and impellers which are arranged in the pump shell body; the impellers are connected to one end of the power shaft, the bearings are connected to the power shaft in a sleeving mode, and the seal rings are arranged between the impellers and the bearings; the water outlet pipe comprises a first vertical pipe, a horizontal pipe and a second vertical pipe, wherein the first vertical pipe is connected with the pump shell body, the first vertical pipe is connected to one end of the horizontal pipe, the second vertical pipe is connected with the other end of the horizontal pipe, and the bottom face of the horizontal pipe is higher than the pump shell body. The backpack portable multipurpose water pump can suck up anytime and anywhere and conduct operations such as efficient and short-time spraying and applying, irrigation and conveying in different places and at different working points, can be used for fire protection, firefighting and fire extinction, spraying pesticide, irrigating and the like under a certain condition or a special condition, and can achieve multiple functions.