Aspherical components have been more and more widely used in optical systems. In order to enhance the ability of light collecting for the optical system, highly steep aspheres are often used. However, manufacturing of highly steep aspheres is now one of the hard work in optical engineering field. Through a manufacturing case of F number of 0.42 off-axis asphere with large asphericity, some researching progresses are introduced. The first is the milling technology for off-axis asphere, comparing with the traditional milling technology of the best fitting sphere (BFS), the remaining asperical error is decreased greatly, and the following grinding cycle is shortened about 2/3; while decreasing the sag difference of the asphere by coordinate transforming of the equation, the difficulty of manufacturing is greatly reduced. Meanwhile, by making the small tool running along the asphere′s normal, we can ensure the removal function′s symmetry, and the solving procedure of the tool′s position and coordinate′s compensation is given in detail. The example shows that the final asphere precision [root-mean-square (RMS)] attains to 0.039λ (λ is 632.8 nm).