The Pseudolite System can independently assist the UAV on precision approach in the case of unavailability of the GNSS. Based on the Pseudolite System, the paper presents some constraints and the method of pseudolites layout for UAV approach guidance in engineering practice. The wide lane combination based on dual-frequency pseudolite signals is established, and the Kalman filter technology is combined for the fast estimation of the wide lane ambiguity. The high precision carrier phase observation is used for the positioning solution. The pseudolite layout design and the positioning simulation are carried out in a typical scene. The results verify the validity of the proposed pseudolites layout method and the correctness of the integer ambiguity determine method, and the positioning accuracy is significantly improved compared with single-frequency pseudorange positioning.