According to the application of GPS differential precise navigation, an ambiguity resolution algorithm is presented. The mathematical model is set up using observations of wide lane double differential carrier phase and double differential pseudorange. In order to make float ambiguity uncorrelated completely, float transformation matrix is constructed by Cholesky decomposition and the integer ambiguity search space is deduced. The criterion of least square residual is used to obtain single-epoch integer ambiguity, OVT (over-the-time) method is applied to verify the consistency of integer ambiguity at different epochs. Experimental results indicate that the mean square deviation of observations has great effect on integer ambiguity's search space and success rate, and the integer ambiguity can be determined correctly and reliably by OVT testing.