The mechanical model of torsional vibration for a V12 diesel engine was established by the concentrated mass method, the calculation was conducted to acquire the load torque excitation of the left and right camshafts of intake and exhaust between 800 r/min and 2 500 r/min, and the forced vibration simulation of camshaft was performed to obtain the torsional vibration amplitude and rolling vibration frequency of camshaft and further analyze the rolling vibration amplitude. The results showed that the 4.5th, 5.0th, 5.5th and 6.5th order mainly contributed to the camshaft forced torsional vibration amplitude. Their peaks reached the maximum at 2 500 r/min and the 3rd order excitation torque constituted the main component of rolling vibration. The optimal harmonic coefficient of the camshaft rolling vibration was analyzed and obtained, the multiple approximate fittings of amplitude results at low speed were conducted to eliminate the rolling vibration error, and the rolling vibration calculation model of the camshaft was established. The calculated amplitude of rolling vibration was close to the 3rd harmonic amplitude of torsional vibration mechanical model between 800 r/min and 1 900 r/min and the difference was less than 0.02 degree. The rolling vibration calculation results met the requirements because the rolling vibration occurred at low speed. Accordingly, the calculation and research conclusions provided the suggestion and reference for the prediction and control of engine camshaft rolling vibration.