Abstract: The resistant level, mechainism of resistance of Alopecurus myosuroides against fenoxaprop-P-ethyl were determined. Results of the whole-plant dose-response test showed that population HN-05 from Henan Province had evolved high-level resistance against fenoxaprop-P-ethyl (52.2-fold). Using the gene sequencing method, two amino acid mutations at codon 2041 (Ile-Asn) and 2096 (Gly-Ala) were detected in the ACCase gene of the resistant population HN-05. Pre-treatment with the known metabolic inhibitor, piperonyl butoxide (PBO), enhanced the activity of fenoxaprop-P-ethyl (161.3-fold). So that the GR₅₀ value (active ingredient) of fenoxaprop-P-ethyl to HN-05 is 5.4 g/hm². This study confirmed the resistance of A. myosuroides against the ACCase inhibitor, fenoxaprop-P-ethyl. The resistance mechanism were conferred by specific ACCase point mutations at amino acid position Ile-2041-Asn and Gly-2096-Ala and P450s-based metabolism.