Cosmic-ray Soil Moisture Observation System (COSMOS) is a new method for measuring mesoscale soil moisture, which can estimate soil moisture within hundred-meter scale by observing neutron counts from soil layers. We summarize the principle of COSMOS observation, analyze the factors including atmospheric pressure, air humidity, solar activity, magnetic intensity, road, and counting neutrons that affect the neutron intensity, review the method inverting neutron counts to mesoscale soil moisture, summarize the spatial weights of in-situ soil moisture calibration samples and the research advancements of observation and application. Also, we used Cosmic-ray neutron rover to measure soil moisture in a desert-oasis regions of Hexi Corridor. The RMSE was 0.03 g/g, and parameter N0 was 690 counts/30s. It demonstrated the rover could be applied to monitor mesoscale soil moisture in the desert-oasis regions. In the desert regions, soil water resources in 0~30 cm depth were 6.8 mm and 19.4 mm in summer and autumn, respectively. In the oasis regions, soil water resources in 0~15 cm depth were 50 mm and 40 mm in summer and autumn, respectively. The research can provide a scientific basis for the evaluation of soil water resources in the desert-oasis regions.