Through the survey of the change of surface layer water vapor, we may investigate newborn and developing process of meso-microscale thunderstorm system, furthermore, we may carry out the short-period forecast of meso-microscale synoptic process according to the water vapor data. Therefore, the water vapor survey is of great value to the research and application. Our research and experiment have shown that widely deployed SA radar can be utilized for measurement of atmospheric refraction index field and further can infer the change of water vapor. This article discuses some key technology of the detection by SA radar.This research may extend detecting capability of SA radar which compensates the insufficiency of ground water vapor information and help study the relationship of meso-microscale convection system evolution to water vapour field change.It can also be expected to improve forecast capability of meso-microscale system in numerical model.