Abstract: Based on the water and soil cultivation experiments on rice and the root growth model of water spinach and lettuce,a model to describe the cycle and characteristics of the root growth of rice was established.Statistical significance of the model for 7 rice varieties was obtained.For instance,the model could predict the root length growth constant,the maximum root growth rate and length,as well as the time for their appearances.The water and soil cultivation experiments showed that all varieties retained a large root system at later stage of growth;no significant difference on root growth characteristics among the late rice varieties,except Teyou 3101;the variation coefficient of the maximum root growth rate among different species was 7.6%;and the time for the maximum root growth was about two months after sowing,suggesting an advantage of topdressing at this time for fertilization efficiency.The soil cultivation experiment showed that the root growth constant could be increased 57.2% by application of a balanced fertilization of nitrogen,phosphorus and potassium,as compared with no fertilization.The maximum root growth rate and root length were increased 61.0% and 65.4%,respectively,showing the apparent effect of the timed fertilization in promoting growth and increasing length of the roots for rice.