2026AJ....171..121X

Chinese Space Station Telescope (CSST), which will begin its scientific operations around 2027, is going to survey the sky area of the median-to-high Galactic latitude and median-to-high ecliptic latitude. The high astrometric precision of the CSST Survey Camera for faint objects enables the detection of a number of giant planets and brown dwarfs around M dwarfs and brown dwarfs via differential astrometry in its optical survey. In this paper, we predict the number of giant planets and brown dwarfs around stars and brown dwarfs detectable with CSST astrometry. We generate synthetic samples of CSST stellar and substellar sources, and carry out companion injection-recovery simulations in the samples using different occurrence rates for FGK dwarfs, M dwarfs, and brown dwarfs. We calculate companion yields based on CSST astrometric precision. Our analysis reveals that over its 10 yr mission, the CSST Survey Camera could barely discover giant planets and low-mass BDs around FGK dwarfs, but is projected to detect 20-170 giant planets and low-mass brown dwarfs around M dwarfs within 300 pc, and 300-570 brown dwarf binaries within 600 pc. Therefore, CSST astrometry is likely to significantly increase the current sample of substellar companions around M dwarfs and brown dwarfs. This sample will deepen our understanding of planet formation and evolution around low-mass stars and brown dwarfs.