Abstract: In order to improve the herbicidal activity of toxins Ⅲ (2-methyl-3, 5-dinitrobenzoic acid methyl ester) from Phoma herbarbum, their structure were optimized by derivation. 34 novel title compounds were synthesized by nitration, esterification starting from o-toluic acid as the starting material. Their structure were characterized by IR, 1H NMR and GC-MS. The screening of the herbicidal activity showed that the inhibition rates of the target compounds on the roots of weed were higher than that of the shoots. The inhibition rates of 4-15, 4-16 and 4-26 against Amaranthus retroflexus root were 92.8%, 92.0% and 87.4% at 100 μg/mL, respectively, which demonstrated significant herbicidal activity. The fresh weight efficacy of 4-1 against Digitaria sanguinalis and A.sretroflexus was 100% at 1 000 g a.i./hm2, which illustrated high herbicidal activity. The ED50 value for D. sanguinalis was 94.89 g a.i./hm2.