Abstract: Soil water plays an important role in the critical zone water cycle, and the results of soil water content observation can in some way affect the allocation of water resources, determination of agricultural practices, and development of environmental disaster forecast. Cosmic ray neutron probe (CRNP)method, which measures soil water content by monitoring the change of neutron current in the near surface cosmic ray, has advanced rapidly in the last decades. The fundamental theories of using CRNP into soil moisture monitoring are introduced. The method has a support volume at hundred-meter (horizontal)and decimeter (vertical)scale, which fills the gap between field sampling and remote sensing. The sensor response is not only influenced by soil water, but other hydrogen reservoirs near land surface, and even within the support volume these factors still don't contribute evenly. Therefore, interpretation of the sensor response, which includes determination of the exact range of the support volume, allocation of spatial weighting factors within the support volume, and calibration of the impacts of atmosphere, soil and vegetation, remains the critical work during the development of the method; and a number of researchers have continuously contributed on it. The current utilization of the method in agricultural management, hydrological modeling and meteorological forecast is enumerated, and existing problems and possible development directions in future are also discussed. By the synthesis of the related work, it is expected to promote a further and extensive application of this method into the above areas.