The invention belongs to a herbicide for preventing and weeding 
dicotyledon weeds and barnyard grasses in paddy fields, relating to a mixed herbicide which has the effective 
active components of carfentrazone-ethyl, pyrazosulfuron-ethyl and 
quinclorac. The mixed herbicide comprises the effective 
active components, moist additive, filler and the like, and is characterized in that the effective 
active components are the carfentrazone-ethyl, the pyrazosulfuron-ethyl, the 
quinclorac, preparations with different contents thereof and various dosage forms, wherein the carfentrazone-ethyl, the pyrazosulfuron-ethyl and the 
quinclorac have the ratio by weight of 1:(1-2.5):(15-40). The invention has the advantages that after being mixed, the carfentrazone-ethyl, the pyrazosulfuron-ethyl and the quinclorac have obvious effects of synergism and enhancing 
weed control speed, obtains 
control effect to various broadleaf weeds and the barnyard grasses in the paddy fields, has 
low toxicity and low residual, expands the 
weed control spectrum, greatly lowers the 
drug dosage, the 
pesticide application frequency and the 
drug cost, and is beneficial to retarding the succession velocity of 
weed populations and prolonging the service life of the herbicide.