The invention belongs to pesticide fields, and in particular to a kind of pyrazolone compound or its salt, preparation method, a kind of herbicidal composition and its application. Pyrazolone compound Formulas I as described above:In the formula, R1R2N indicates the substituted or unsubstituted heteroatomic 3-8 member heterocyclic ring containing nitrogens group containing 1-3 Or R1 and R2 respectively represent hydrogen or C1-8 alkyl R3 represents hydrogen, C1-4 alkyl, alkenyl, alkynyl, unsubstituted C3-6 naphthenic base or C3-6 alkyl C1-4 naphthenic base quilts R4 represents methyl, ethyl, n-propyl, isopropyl or cyclopropyl X represents hydrogen ,-S (oxygen) nR6 -R7 or substituted or unsubstituted 3-8 element heterocycles base contain 1-4 hetero atoms n represents 1,2 or 3, and R6 represents substituted or unsubstituted alkyl or aryl, and R7 indicates substituted or unsubstituted alkyl, aryl, alkanoyl or aroyl. Active material of the invention shows that interests herbicidal effect is good, easy to use, low in cost, has great commercial value.
