Abstract: Deep space exploration tasks are developing rapidly both at home and abroad. In recent years,a number of new deep space probe projects have been proposed,which are adopted modular design and on-orbit assembly and maintenance. On-orbit assembly and maintenance are the basic contents of spacecraft on-orbit service technology. Foreign countries have achieved fruitful results after decades of development in this field,and modular design is a major supporting technology for on-orbit assembly and maintenance of spacecraft. In this paper,the modular design and on-orbit assembly and maintenance programs in the deep space exploration are summarized,mainly including modular exoplanets landing probes,large on-orbit assembly deep space probe,the very large on-orbit assembly space telescope system in the SEL2 orbit,and so on. The key elements of the deep space probe modular design for the on-orbit assembly and maintenance are analyzed. At the same time,aiming at the technical requirements of long life,high reliability,special propulsion system and its supporting equipment of deep space exploration spacecraft,a multimission Mars probe system is proposed,which applies the on-orbit assembly and maintenance technology. The mission framework, the basic composition and the orbit strategy of the probe system are introduced. The above investigations and analyses will provide the reference for the development of the deep space detection technologies and the development of new deep space probes in China.