Results of two years experiment showed that a lot of grass in paddy field could be prevented by spray of 26% MCPA and Bentazone EW, such as: Monochoria korsakowii Regel et Maack., Sagittaria sagittfolia L., Alisma orientale（Sam.） Juzepcz., Bidens tripartite L., Scirpus juncoides Roxb., Scirpus planiculmis Fr. Schmidt., etc. The control effects reached 90%. The optimum dosage was 585 g per hectare when nutgrass flatsedge was less than 50 per m². The dosage ranges 702 to 780 g when nutgrass flatsedge was more than 50 per m². The herbicide was applied 20 to 30 days after transplanting. Water was drained off before spraying. The chemical was dissolved in 450 kg of water per hectare.