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Successful resolution of cycle ambiguities plays a crucial to high accuracy and high integrity navigation by carrier phase differenced positioning architecture. However, a cycle slip caused by loss-of-lock of signal changes the fixed ambiguity, which will affect the cycle resolution integrity. It is, therefore, necessary for detecting cycle slip and further satisfying its integrity. In general, dual frequency measurements are deployed to construct the carrier phase differenced positioning architecture for satisfying the stringent accuracy and integrity performance for safety-critical applications, such as automatic shipboard landing. Thus, dual-frequency-based cycle slip detection methodologies can be introduced in this positioning architecture. The geometry-free (GF) modeling uses only dual-frequency phase measurements to construct the statistical residuals, which are sensitive to small cycle slips that should be detected in high-integrity applications. At present, the threshold of the GF modeling is generally designed as an empirical constant, such as 5 cm, lacking theoretical derivation to quantify its integrity risk. Therefore, this paper proposes an integrity monitoring method for GF modeling to satisfy the integrity performance. Determining the threshold value of the cycle slip statistical test is designed as a function of a required false alarm probability and the quality of raw phase measurements. A required missed detection probability can be used to construct the minimal detectable error (MDB), which can evaluate the availability of the integrity monitoring method to control the missed detection probability. As noted above, the threshold and the MDB are jointly deployed to provide the high-integrity requirements. This paper collects simulated and real-world dual-frequency GNSS datasets to verify the performance of the proposed method. The results show that this method can dynamically adjust the detection threshold to control the false alarm probability and adjust the MDB to evaluate the availability of the integrity monitoring method to control the missed detection probability. Consequently, the proposed integrity monitoring method of cycle slip detection can effectively satisfy the high integrity requirements of cycle slip detection.