The invention belongs to the field of automobile part producing and assembling, and particularly relates to assembling equipment for a DCT gearbox shaft system. An automatic assembling device for the DCT gearbox shaft system comprises an assembling rack, an input shaft assembly fixing mechanism, a first output shaft assembly assembling mechanism, a second output shaft assembly assembling mechanism and a differential mechanism assembly assembling mechanism, wherein the input shaft assembly fixing mechanism comprises a fixing device used for fixing the shaft center of the input shaft assembly, and a motor used for driving the input shaft assembly to automatically rotate; and an output end of the motor is connected with the fixing device. The automatic assembling device for the DCT gearbox shaft system can realize automatic assembling of the shaft system before the DCT gearbox shaft system is subjected to mould assembling, is high in precision of an assembling position, avoids the artificial collision defect, and increases an assembling qualification rate.