<p>Dual-antenna orientation is one of the main applications of the global navigation satellite system, the basic principle of which is to determine the direction of the spatial vector formed between two antennas by utilizing the interference of carrier signals. For ultra-short baseline situations with lengths less than 1m, current research on dual-antenna orientation mostly uses a wide-lane combination of carrier phase, which improves the success rate of integer ambiguity resolution. However, it will amplify errors due to longer carrier wavelengths, resulting in lower orientation precision. An improved least squares ambiguity search method was proposed to solve this problem. The process was based on baseline lengths and satellite geometry constraints, and the narrow-lane combination technique of the carrier phase was adopted. The baseline length is used as a constraint to limit the ambiguity search space, enabling real-time calculation of the heading angle in a single epoch. The experimental results show that this method can fix the ambiguity quickly and accurately in several situations, including single-system single-frequency, single-system dual-frequency, and multi-system multi-frequency. With a baseline length of 0.5 m, the orientation precision achieves 0.26° in a static open environment, within 0.30° in a static blocking environments, and around 0.54° in a dynamic environments.</p>