Abstract: Against the current situation of centering instrument with low precision and dependent on the human eyes, a research method of high-precision centering instrument based on position-sensitive detector (PSD) was put forward. Through the use of self-collimated optical path and PSD, the return light spot from the target was located, and the coordinate value on the computer was read to judge whether the accurately centering was achieved. The design of the centering instrument optical system and the nonlinear correction of PSD by neural network training were carried out. Results show that t can achieve the design requirement of centering accuracy with measuring range of 2 mm~500 mm, which is much better than traditional centering instruments.