Abstract: Guide star selection is a crucial part of star tracker design. For thin field-of-view star tracker, guide star catalogholes are common as stars are not evenly distributed. To optimize the guide star selection for star tracker with thin field of view, the selection method based on spherical spiral points was modified. Building a new guide star catalog by increasing the number and changing the positions of spherical spiral points, which was usually adopted, was abandoned. Some new stars which can effectively decrease guide star catalogholes into the guide star catalog were proposed. The weights to measure stars' ability of decreasing guide star catalog holes were constructed and the adding star process was carried out on the order of the weights descending. And the new star added into guide star catalog was required far away from the guide stars to keep the guide stars even. Simulations expressed that the modified method got less and evener guide stars than the original method with similar guide star catalog holes, which shows the superiority of the modified method.