Rice is a vital world food crop, and most paddy rice fields distribute in warm, humid environmental regions with heavy cloud cover and rainfall. It is difficult to acquire optical remote sensing data in these regions. So SAR system is used to map and monitor rice crop growth status. It is important for rice monitoring to understand the microwave backscattering. The backscattering is related to the dielectric properties and geometric parameters besides the radar system parameters. The geometric parameters of the rice can be easily measured, but it is very difficult to get the dielectric constant from ground observation due to many influence factors. So it is necessary to compute the dielectric constant using models.\;This paper presents the modeling results of dielectric constants from different rice growth stages in Zhaoqing test site using Debye_Cole dual_dispersion mode of vegetation. In the test site, two crops of early season rice and late season rice are planted in 1997 and 1996, and the growing period of rice crop is divided into five major stages: transplant, seeding developing, ear differentiation, heading and mature period. Based on the results, the paper discusses the influences from microwave frequency, gravimetric moisture content of rice, temperature, salinity and bulk density of dry vegetation meterials on dielectric constant. The rice crops of different growth stages have the various dielectric constants, and the dielectric constants of early and late season rice crops show the diverse changes. The parameters, including microwave frequency, gravimetric moisture content of rice, temperature and bulk density of dry vegetation materials, have the influence on dielectric constant, but salinity has no effect on the dielectric constant.