Aiming at the design problem of the three-axis photoelectric tracking system for space target acquisition, firstly, the error source that affected the three-axis photoelectric tracking system to capture the space target was analyzed, and the main error was estimated, that was, track prediction error and three-axis pointing error. Then the error propagation relationship from the main error to the field of uncertain (FOU) was established, the uncertain area was calculated by using the transfer relation, and the search scanning mode was designed according to the size, shape and distribution type of the uncertain area. Taking an example of the shape of the field of uncertain as an ellipse and obeying the two-dimensional normal distribution, the design of the search mode was the branch spiral scan. Finally, the numerical simulation was also carried out to verify the correctness of the mode. By simulation calculation, the average acquisition time of the target was 10.52 s in the case of the capture probability of 98%. This mode provides a theoretical basis for the acquisition of space targets by three-axis photoelectric tracking system.