Due to the big position error and strong limitations by using high odd polynomial method and optical refraction model, an optimization of fisheye lens imaging position algorithm is proposed. A new distortion model is derived according to the decentering distortion of the lens and optimized imaging model is established based on the distortion model and optical refraction model. After calibrating the imaging model parameters, a back projection model is derived and then three dimensional point coordinates are obtained. Space targets are precisely positioned. Experimental results show that the proposed algorithm has far less relative positioning error than the method which using high odd polynomial and optical refraction when the measured object respectively in fisheye image center and edge areas. Compared with previous method, the image distortion of proposed algorithm obviously has less influence on measurement precision and it effectively improves the positioning accuracy.