On the basis of application of GPS carrier phase measurements to determinate the carrier's attitude, focusing on its key technical problem—fast determination of carrier phase ambiguity,a method which makes full use of geometric constraints among GPS satellites and baseline to compress search space in order to acquire the correct double differential ambiguity quickly has been developed. A simulation experiment using the rude statistics received by ADUⅡ attitude determination receiver shows that it is a practical ambiguity resolution.