Estimation of agricultural damage caused by natural disaster is necessary. It is important to establish a method of monitoring the damage of paddy fields by natural disaster such as a volcanic eruption, an earthquake or flooding. Synthetic Aperture Radar (SAR) is one of the important remote sensing technologies. SAR actively radiates microwave and receives microwave reflection from various objects. Compared with optical remote sensing technique, we can analyze image without the effect of clouds and observe the surface of the earth in day and night. SAR microwave has different character for its wavelength. These characteristics are suitable for analysis of agricultural disaster for various situations. Actually, SAR is used in many scenes, for example, to measure the damage of a typhoon-fed flooding and a quake-triggered landslide. Water level drop of paddy fields caused by an earthquake is also a serious problem. In this study, we consider the way to measure the degree of water level drop by using SAR data. Specifically, we compared SAR intensity difference between the images obtained before and after the earthquake. Then we succeeded to measure the degree of water level drop.