In this paper,56% MCPA-Na SP(2-methyl-4-chloro-phenoxyacetic acid-Na salt powder) was applied to investigate the control effects of Monochoria vaginalis (Burm.F.),Cyperus difformis L., Eclipta prostrate L. and the influence of weed control on nutrition and crop yield of rice. The results showed that 56% MCPA-Na SP had good control effects on broadleaves and sedge weeds.The overall quantitycontrol effects reached 85.50%-94.48% and the overall fresh control effects reached 88.20%-94.87%.The application of 56% MCPA-Na SP significantly reduced the weeds absorption of nutrition and water,resulting in prominent yield enhancing.