The invention relates to a power device for a spreader and a using method of the power device, and belongs to the technical field of power mechanical equipment. According to the power device and the using method, the spreading width and the spreading density are guaranteed when an engineering van is at different speeds, and the spreading quality and the work efficiency of the spreader are improved. The power device comprises a stepless speed changing mechanism, an installation base and a pulling wheel, the stepless speed changing mechanism comprises a first speed changing wheel, a second speed changing wheel, a first spline shaft, a second spline shaft, a V-type belt, a first shifting fork and a second shifting fork, and the first speed changing wheel and the second speed changing wheel are connected through the V-type belt. The using method of the power device comprises the following steps: placing the spreader in a cargo hopper of the engineering van, enabling the installation base of the power device to be fixed on a chassis of the engineering van, using the engineering van to carry and convey the spreader to a road where the spreading operation will be carried out, enabling a piston rod of a hydraulic cylinder to be lengthened, enabling a second supporting arm to drive the pulling wheel to drop to the ground, starting the engineering van to walk at a constant speed, and driving a gear pump through the stepless speed changing mechanism to rotate to provide power for the spreader.