A series of novel triazolinones were synthesized and their structures were characterized by (1)H NMR, elemental analysis and single-crystal X-ray diffraction analysis. The herbicidal activities were evaluated against Echinochloa crusgalli (L.) Beauv., Digitaria adscendens, Brassica napus and Amaranthus retroflexus. The herbicidal activity data indicated that the title compounds had higher activities with substituted benzyl group moieties than with other groups such as sulfonyl, alkyl, etc. To further investigate the structure-activity relationship, comparative molecular field analysis was performed on the basis of herbicidal activity data. Both the steric and electronic field distributions of comparative molecular field analysis are in good agreement in this work. The results showed that a bulky and electronegative group around the ortho- or para-positions of the benzene ring would possibly lead to higher activity. Based on the comparative molecular field analysis, compound I-23 was designed and synthesized, which display as good herbicidal activities as the commercial herbicide, carfentrazone-ethyl. The activity against Digitaria adscendens is 66.1% under pre-emergence at 300 g of a.i./ha.