Abstract: We verified three enzyme mechanisms of resistant biotype Avena fatua L. against Haloxyfop-Pmethyl, in order to provide a basis for controlling and delaying weed resistance. We tested the difference of ACCase, CYP450 reductase and GSTs activities in Haloxyfop-R-methyl resistant and sensitiveA vena fatua L. biotypes by potting method in greenhouse. The results showed that: the ACCase activity of resistant biotype Avena fatua L. was lower than that of sensitive biotype when herbicides were not applied; with the increase of Haloxyfop-R-methyl concentration, the activity of 2 biotype ACCase decreased gradually, but the decrease of there sistant biotype wasless than that of the sensitivebiotype, the two ACC aseactivity IC50 valuewas78.369μmol/L and 43.469 μmol/L, respectively, and the active multiple was 1.8; there was no significant differences in the activity of CYP450 reductase and GSTs between the resistant biotype and sensitive biotype of Avena fatua L. under water treatment; the activity of the resistant bio-type CYP450 reductase and GSTs was higher than that of the sensitive biotype after the application; after 12 days of application, the content of the resistant biotype and the sensitive biotype CYP450 reductase was 113.1 pmol/L and 38.9 pmol/L, respectively, the activity multiple was 2.91, and the 2 biotypes’GSTs activity was 210.6 mIU/L and 319.1 mIU/L, respectively, and the active multiple was 1.52. The high level of target enzyme activity and the enhancement of metabolic enzyme activity are important mechanisms for the resistance of Avena fatua L. to Haloxyfop-P-methyl.