Ionospheric storms and scintillation cause great impact on the service performance of single-frequency Satellite-Based Augmentation System (SBAS). On the one hand, conservative estimation method of the ionospheric integrity information can lead to the problem of over-wrapping in the pseudorange domain and cannot make it optimal to the service performance of SBAS. On the other hand, the performance of the ionospheric Kriging method is unstable in some regions with active ionospheric. Meanwhile, there will be a growing number of dual-frequency users with the development of GNSS. This paper proposes IFree Filter-based user positioning algorithm for SBAS and analyzes the positioning performance of 36 Monitor stations in North America. First, high-order differential method is used to detect cycle slip of dual-frequency carrier-phase observation, and chi-square test is used to detect and eliminate outliers. Then, the dual-frequency pseudorange is smoothed with the dual-frequency carrier phase after cycle slip repair, and the ionospheric delay is treated with IFree filter. Compared with the Wide Area Augmentation System (WAAS) algorithm, the signal-in-space correction accuracy by the proposed algorithm is significantly improved, which can provide LPV200 services for most regions in North America and even CAT-I services for some regions, and can be applied as key technologies to monitor stations and information processing center of the civil services platform for BeiDou Satellite-Based Augmentation System (BDSBAS).