Abstract: Multi-satellite precision Orbit Determination and data Analysis Software in solar system (MODAS) is produced by the orbit dynamics group at the Science and Technology on Aerospace Flight Dynamics Laboratory. It provides an efficient and uniformed approach to perform orbit determination for spacecraft in solar system. In addition, it is aimed at solving the joint orbit determination of multiple spacecraft orbiting different celestial bodies, and can be used for both scientific application analysis and engineering practice. This paper describes the design and implementation of MODAS, including data organization and management, fundamental services, measurement models, and parameter estimation. Then, the implementation characteristics of MODAS are introduced in detail. The function is validated through the exploration data processing of the moon, Mars, Jupiter and asteroids. Finally, further application and improvements of MODAS is discussed.