Abstract: Based on self-developed software, a GPS real-time attitude determination system is built using GPS OEM boards as basic hardware. The Hardware structure is simple and the cost of system is low. The attitude determination software solve a series of technical problems such as data receiving, decoding and synchronizing, carrier phase ambiguity resolution, system kinematic calibration. Validated by static and kinematic experiments, the system run stably and has well dynamic performance. The mean square error of attitude can be less than 0.3? when baseline length be 1.2m around. So the system can act as navigation equipment or as regulator of navigation equipment.