Assembled hollow camshaft can be manufactured through hydrojoining process which has the advantages including joining multiple elements onto a tube in once loading, high joining strength, efficiency, and precision. The method of improving joining strength by using cams with noncircular hole was presented. Through numerical simulation and experiment, plastic deformation law of hydrojoining process was studied. The displacement of cam and tube, and the profile dimension change of cam during hydrojoining were obtained. The effect of hole shape of cams on joining strength was analyzed. The assembled hollow camshafts with casting iron cams used for a car engine and those with quenched steel cams for a truck engine were successfully manufactured using hydrojoining technology.