The present invention belongs to the field of pesticides, particularly relatesto a pyrazolonecompound or a salt thereof, a preparation method therefor, a herbicidalcomposition and usethereof. The pyrazolone compound is as described in formula I:(See Formula I)In the formula, R1R2N represents substituted or unsubstituted 3-8 memberednitrogen-containing heterocyclic group containing 1-3 heteroatoms； or R1 andR2 eachrepresent hydrogen or C1-8 alkyl； R3 represents hydrogen, C1-4 alkyl, alkenyl,alkynyl,unsubstituted C3-6 cycloalkyl or C3-6 cycloalkyl substituted by C1-4 alkyl； R4represents methyl,ethyl, n-propyl, isopropyl or cyclopropyl； X represents hydrogen, -S(O)n R6, -R7 or substitutedor unsubstituted 3-8 membered heterocyclic group containing 1-4 heteroatoms,wherein, nrepresents 1, 2 or 3, R6 represents substituted or unsubstituted alkyl oraryl, and R7represents substituted or unsubstituted alkyl, aryl, alkyl acyl or aroyl. Theactive substanceof the invention exhibits good herbicidal effect, and is convenient to use,low in cost and hasgreat commercial value.
