The invention relates to an automobile coating production line, in particular to a pitch changing device and a using method thereof when primer and finish paint of the automobile coating production line adopt components with different lengths and different skid systems. Through the implementation of the pitch changing device, the problem of inconsistent positions and sizes of a cab and a cargo compartment on two skids of the primer and the finish paint is solved, the conversion of the cab and the cargo compartment on the two skids is smoothly realized, the production requirements of the cab and the cargo compartment on a primer line and a finish paint line are met, and the investment of the primer line on a vehicle body can be reduced by about 6%.