A 3D measurement system of complex deep-hole profiles based on ring-structured-light was presented. By analyzing disadvantages of the original system, such as nonlinearity between the input and output, the exterior and the interior stripe points of the image belonging to different measured profile in once measurement and existing occlusions due to rifling, an improved scheme was proposed, in which the half-angle of the conic mirror was changed from 45o to 50.7o. In the meantime, related parameters of the measurement system were also adjusted. The improved system eliminates nonlinearity error, which increases measurement accuracy. The exterior and the interior stripe points belong to the same measured profile, and one side of the occlusions of the exterior stripe is eliminated, which can increase the efficiency and the accuracy of 3D reconstruction.