Abstract: We propose a new integer ambiguity resolution method,which enables one to determine DD carrier phase integer ambiguities at single epoch on the fly.Then receiver autonomous integrity monitoring(RAIM) based on carrier phase is researched.Test statistic is constructed using the method of least squares to test the integer ambiguity.Relationship between protection level,satellite geometry and miss detection probability is analyzed.Experiment results indicate that the success rate of integer ambiguity is 100% at single epoch on the fly.By adding one observation satellite,the vertical protection level will reduce about 0.2 m,the test statistic can detect cycle slips with 100% success rate.