The assembly assembly of engine crankshaft rear oil seal comprises a positioning connection and mutual adaptation base and rear oil seal seat, and also includes a guide sleeve and a pressure sleeve. The crankshaft rear oil seal is mounted on the inside of the rear oil seal seat through the guidance positioning of the guide sleeve and the pressure action of the pressure sleeve. The rear oil seal seat is in the shape of a step, and the base is provided with a groove. The size of the bottom of the lower step of the rear oil seal seat is matched with the groove. A circular hole is arranged in the middle of the base, and the guide sleeve is installed and positioned in the circular hole; The pressure sleeve is fitted on the outside of the guide sleeve and matched with the clearance. The pressure sleeve presses the crankshaft rear oil seal on the lower step inside the rear oil seal seat through the guidance positioning of the guide sleeve. The base and the rear oil seal seat are fixed by the positioning pin. The locating pin is a locating round pin or locating rhomboid pin. The assembly component of the utility model solves the problem of difficult pressing when the oil seal is pressed into the inner side of the step shaped rear oil seal seat. And to ensure the assembly of oil seal flatness, pressure depth and other assembly requirements. The assembly efficiency of the rear oil seal is improved, and the precision and quality stability of the product are improved.