Abstract: ObjectiveInfluence of Leptochloa chinensis(L.)Nees. on the growth and yield properties of rice and its control economic threshold were studied in order to provide technical guidance for the scientific control of L. chinensis in rice field.MethodThe effects of different densities of L. chinensis(0,1,2,5,10,20,40,80 plant/m2)on light penetration rate of rice,absorption of water and nutrition,yield properties of rice were investigated in field conditions. Then the func-tional relationship between different densities of L. chinensis and rice yield loss rate was researched by using model fitting method. Finally,economic thresholds for control of L. chinensis were derived on the basis of economic infestation levels (EIL).ResultWith the increasing density of L. chinensis,its plant height increased significantly(P<0.05,the same be-low). L. chinensis competed for the light in rice field with advantage of plant height. When the density of L. chinensis was≥10 plants/m2,the light penetration rate at 70 cm above the ground was less than 10.00%and at 25 cm was less than 1.00%. At the same time,L. chinensis competed with rice for water and nutrition in the soil of rice field,which affected the growth of rice and decreased yield properties of rice such as effective ear number,ear length,full grain number and weight of 1000 grains. The rice yield sharply decreased and rice yield loss rate increased. The result of correlation analysis showed that among all yield properties of rice,except ear length and blighted grain number had no significant correlation (P>0.05),the correlation of other yield properties all reached significant level or extremely significant(P<0.01)level. The quadratic curve model(y=-0.0151x2+2.276x+0.8114)could well fit the relationship between the density of L. chinen-sis and rice yield loss rate. According to EIL and the quadratic curve model,the economic threshold for artificial control of L. chinensis was 5.39 plant/m2,and the economic threshold for chemical control by 10% cyhalofop-butyl EC was 0.76 plant/m2.ConclusionL. chinensis competes with rice for light,water and nutrition of soil in the rice field,and affects the yield properties of rice,resulting in the serious yield reduction. Chemical control for L. chinensis has obvious economic ad-vantage.