Abstract: Two or more GPS receivers can be used to determine the orientation or attitude of objects except that GPS can be used to determine the position, velocity and time. How to determine the orientation precisely based on carrier phase synchronization provided by two GPS OEM boards is studied in depth in this paper. The double difference of carrier phase is formulated first and then the orientation and pitch are searched in two dimensional space based on the baseline between the two GPS receivers. The ambiguity function is used as the judgment criterion to search the azimuth and pitch. At last, the baseline vector of the two GPS receivers is determined using the least square and the accurate azimuth and pitch are calculated based on the accurate baseline vector. Many test results show that the method is feasible and the accuracy can reach 0 08 degree with a 5 meters baseline and it only takes 1 3 minutes to determine orientation in real time.