Based on interferometry measurement theory of satellite carrier phase, the technology of land vehicle heading determination through Beidou Bi-Satellite System was studied. Firstly the mathematical model of Beidou heading determination was set up. Then the ERMM (Equivalent Rotating Maximum/Minimum) ambiguity resolution method based on antenna swap thoughts was discussed. Vehicle real-time heading resolution experiments were designed by using a two-antenna pointing system, and the heading precision was verified through a vehicular RLG (Ring Laser Gyro) strap-down INS with high attitude accuracy. The test results confirmed the effectiveness of ERMM ambiguity resolution method with the real-time heading determination accuracy reaching 0.62 degree. The research indicates that Beidou Bi-Satellite System can be used to real-time land vehicle heading resolution.