Abstract: The action mechanism of N-(3-chloro-5-(trifluoromethyl) pyridine-2-methyl-2, 3, 5, 6-four fluorine-4-methoxy benzamide(LH-2010A) against Phytophthora capsici was investigated. Bioassay method was adopted to determine the toxicity of LH-2010A against mycelial growth, zoospores release and mycelial yield of P. capsici. Morphology and ultrastructure of mycelial treated with LH-2010A were studied. Mycelial respiration rate test was also conducted to evaluate the inhibition effect to metabolic approaches, including embden-meyerhof-parnas(EMP), tricarboxylic acid cycle(TCA) and hexose monophophate(HMP). The effect of LH-2010A on the permeability of the cell membrane, protein biosynthesis and DNA biosynthesis were determined. The results demonstrated that inhibition effect to P. capsici by LH-2010A was observed at different stages in the life cycle of P. capsici, including the mycelial growth, the zoospores release and the mycelial yield, with EC50 values of 7.14, 16.34 and 5.12μg/mL, respectively. Morphological and ultrastructural studies showed that LH-2010A caused the excessive branching and swelling of hyphae as well as the development of a thicker and multilayer cell wall. The inhibition of LH-2010A on mycelial growth was reduced by the addition of ATP, which suggested that the action mechanism of LH-2010A was connected with impairment of the energy generation system. Specifically, the approach of TCA was inhibited by LH-2010A significantly. The conductivity of mycelia cell suspension increased in the presence of LH-2010A, which indicated that LH-2010A affected the cell membrane permeability. The relative leakage of mycelia cell suspension treated with 100μg/mL LH-2010A for 400 minutes was 78.23%. However, LH-2010A had little effect on the biosynthesis of protein and DNA. These results suggested that LH-2010A exhibited multiple modes of actions including the impairment of the energy generation system and the influence on the cell membrane permeability directly or indirectly.