Abstract: Rice stem maggot, Chlorops oryzae Matsumura, is one of the key insect pests of rice in mountain and semi-mountain area in southern China. Based on the studies and investigation in paddy fields from 2000 to 2005, the pattern of occurrence, key factors affected its population dynamics and rice yield losses were preliminarily proved, and its control threshold was recommended at peaks of adults occurred and eggs hatched, when 10 eggs were found in 100 seedlings or more than 1% plants were damaged at seedling stages and average 1 egg laid in one hill or 3-5% plants were infested. Field investigation on distribution pattern of rice stem maggot showed that the eggs distributed evenly and the larva aggregated, and then the sequential sampling and simplified field investigation techniques, and population monitoring and forecasting methodologies GIS-based were proposed and the systems of data pool management, population stepwise regression, and the simulating model of population dynamics were constructed. By improving the population monitoring and forecasting methodologies, the modified systematical management strategies, focused on the first generation to suppress the population number of second generation, integrated with agricultural, physical and chemical managements, had played significant role in decreasing the population density of rice stem maggot and increasing the economic, social and ecological profits in southern China.