The invention relates to a 4-substituted phenyl-6-trifluoromethyl-2-amino pyrimidinamine compound which has a novel chemical structure and a general formula III, a synthesis method for the compound and the application of the compound used as bacteriacide. The method comprises the following steps of: reacting substituted phenyl methyl ketone used as an initial raw material and trifluoroacetic acid ethyl ester under catalysis of sodium alcoholate to generate 4,4,4-trifluoro-1-substituded phenylbutane-1,3-diketone, and reacting 4,4,4-trifluoro-1-substituded phenylbutane-1,3-diketone and guanidinium salt under an alkaline condition to generate a III series compound with the general formula III. The compound with the general formula III can inhibit growth of pathogenic bacteria such as rice sheath blight, rice bakanae disease, exserohilum turcicum, bipolaris maydis, curvulavia lunata, corn kernel rot, corn top rot pathogenic bacteria, fusarium graminearum, cotton anthracnose, bean fusarium, rape sclerotinia rot, botrytis cinerea, cucumber fusarium wilt pathogenic bacteria, cucumber brown rot pathogenic bacteria, cucumber scab pathogenic bacteria, hot pepper root rot pathogenic bacteria, kidney bean anthracnose bacteria, and pythium aphanidermatum. In the formula III, R is methyl, ethyl, methoxy group, fluorine, chlorine, bromine, trifluoromethyl and other groups, and the number of R is 1 to 3.