Abstract: The basic principle of autoguiding was introduced in detail, which included the proper star selection and tracking algorithm. Considering that the star energy distribution in the image was approximately Gaussian distribution, a reliable target star selection method was proposed. The algorithm analyzed a threshold value of the image firstly, and then a number of candidate stars were detected according to the threshold condition. The target star was selected from the candidate stars by guiding criterion. Finally, the centroid coordinate of the target star was calculated through Gaussian fitting. The accuracy of the target star detection and calculating speed were both improved, the experimental results showed that the proposed algorithm can achieve a good autoguiding performance.