Due to the limits of light sources,the sizes of rotating platforms and the propagation of assembling errors,traditional methods of lens centering are not suitable for the assembly of large-aperture and multi-lens optical systems.Thus a new high-precision mechanical measurement method for lens centering was proposed based on a three Coordinate Measuring Machine(CMM).Principles and algorithms for measuring off-centering of the large aperture lens using the high-accuracy CMM were introduced.In the measurements,the angle between the optic axis of lens and the reference axis was calculated after the figure fitting of the measuring points,and then the centering of deviation was calculated.The method was verified by the assembling of a long focal length and large aperture imaging system.The assembling result shows that the lens off-centering is 6.47″ and the repeatability error is(1.16×10-4)″.As changing the optical measurement into a mechanical measurement,this proposed method ensures the accuracy,reduces the difficulty and improves the efficiency of lens assembly.It is able to be applied to the high-precision assembly of large aperture transmitting optical systems.