Abstract: The spectrum of weed control, herbicidal activity and safety to different cotton varieties of trifloxysulfuron, a novel efficient herbicide with low toxicity being used in cotton field, were tested under greenhouse conditions, and pyrithiobac-sodium was used as control. The results indicated that trifloxysulfuron caused ≥90% fresh weight reduction of Cyperus rotundus, Setaria viridis, Eclipta prostrata, Chenopodium serotinum, Erigeron pilosa, Conyza canadensis, Leptochloa chinensis, Bidens pilosa, Xanthium sibiricum, Myosoton aquaticum and Amaranthus retroflexus applied at dose of 11.25 g/hm2(active ingredient dose). There was higher herbicidal activity against C.rotundus, Abutilon theophrasti,S.viridis, A.retroflexusand and Portulaca oleracea than pyrithiobac-soidum with the activity ratio of 171,13.6,12.6,10.5 and 3.82. The selectivity index of trifloxysulfuron between Huamian 5 with C.rotundus, S.viridis and A.theophrasti were 13.0, 2.80, 1.13,respectively, which was higher than that of pyrithiobac-sodium with selectivity index of 2.29, 1.78, 0.86, however, the selectivity index of trifloxysulfuron between Huamian 5 and A.retroflexus, P.oleracea were just 2.80 and 1.74, respectively, which were lower than that of pyrithiobac-sodium with selectivity index of 4.75 and 3.38, respectively. The selectivity index between Shannongmian 8 and the weed species mentioned above was similar to that of Huamian 5.