The invention provides a compost raw material mixing device which comprises a mixing tank, a rotating shaft, a motor, a speed reducer and supporting members, wherein the two ends of the rotating shafthorizontally protrude and extend out of the mixing tank, a driven wheel is arranged at one end of the rotating shaft, the speed reducer is connected with the motor through a first transmission part,the speed reducer can drive the driven wheel to rotate through a second transmission part, the supporting members are arranged at equal intervals in the longitudinal length direction of the rotating shaft, a first spiral body and a second spiral body are arranged on the rotating shaft, the first spiral body and the second spiral body are distributed in a mutually staggered mode and are in mutuallymeshed rotation, the rotating shaft is connected with the first spiral body and the second spiral body through the supporting members, and a starting and stopping device is formed at the bottom of the mixing tank. By means of the compost raw material mixing device disclosed by the invention, a better stirring and mixing effect on the compost raw materials can be achieved; meanwhile, moisture in the final prepared compost raw materials is reduced, sugar in the final prepared compost raw materials is improved, and large particles in the compost raw materials can be further rotary cut and smashed.