Precise determination of formation states provides the foundation for Formation Constellation to carry out its function. In this paper, the state determination problem of double-satellite formation constellation for earth-observation purpose was discussed. On the basis of GPS, a ‘GPS-like’ ranging technology was introduced to improve the state results. Two mathematical models combining ‘GPS-like’ Ranging technology with GPS were built. In this way, a synchronous initialization method for single differential GPS inter-satellite integer ambiguity and single differential ‘GPS-like’ intra-satellite integer ambiguity were also developed. Finally, these models above were simulated and analyzed. The results indicate that, ‘GPS-like’ observation data, especially the single differential ‘GPS-like’ intra-satellite carrier phase data, significantly improved the states results, and the accuracies of absolute attitudes, relative position and relative clock bias respectively reached rad, m and s. The simulation proves that these methods are correct and model II is more accurate than model I.