Through the measurement of radial and axial dimension for cone, the non-contact measurement of taper is realized by using an optoelectronic inspecting system, which is composed of a laser-scanned measuring system, a grating displacement measuring system and a servo control system. Under microcomputer control, the three system make data exchange and control information conveying each other by communicating interface, and synchro control executive mechanism, they can realize the measurement of taper. The two diameters of the cone were measured by the laser-scanned measuring system, the axial dimension of the cone was measured by the grating displacement measuring system, through the computer real-time data processing, the taper of the measured cone was given out. The measured result was displayed or printed output. The measuring method has many features such as high speed, high accuracy and non-contact automatic measurement etc. It has great applicable prospects. In this paper, the measuring method of taper, the overall constitution of the optoelectronic inspecting system and the working principle were discussed in detail, the accuracy of the optoelectronic inspecting system was analyzed, and the practicability of the measuring method was verified by experiments.