Abstract: Geostationary orbit microwave sounding satellites carrying microwave sounders leverage the relatively stationary characteristics of the platform, as well as the microwave’s ability to penetrate clouds and rain, to achieve high-frequency, all-day, and all-weather atmospheric observations. Thus, these satellites provide high-value data for numerical weather forecasting and disaster weather research. This study analyzes the sounding capability of the Chinese Fengyun-4 geostationary orbit microwave satellite, which is currently under development. The observation method and product system are introduced in this paper. The submillimeter wave sounder enables the 55 GHz microwave hyperspectral frequency band and the 380–425 GHz terahertz channel, which are not available on existing low-orbit satellites, greatly expanding the ability of the sounder to observe atmospheric status and cloud parameters. The unique observation geometry characteristics of the satellite are explained through simulation technology in this study. Furthermore, the brightness temperatures of typical channels for detecting temperature and humidity, as well as the terahertz channels, are simulated using the ARMS fast mode and atmospheric backgrounds under a typhoon background.