The invention discloses a method of simultaneously detecting residual amount of dinotefuran and metabolites, UF and DN, thereof in grain. The method includes the following steps 1) extraction: crushing to-be-tested grain sample, adding acetic acid and acetonitrile, performing ultrasonic extraction, adding anhydrous magnesium sulfate and performing centrifugation; 2) purification: placing an upper layer, acetonitrile phase, in a centrifugal tube filled with a matrix solid-phase dispersion extraction agent, performing centrifugation to obtain a supernatant, blow-drying the supernatant with nitrogen, and diluting the mobile phase to a constant volume; and 3) measurement and result calculation: detecting the sample liquid to measure chromatographic peak area, substituting the chromatographic peak area into a standard curve to obtain the content of the dinotefuran and/or the UF and/or the DN, and calculating the residual amount. Through the solid-phase dispersion extraction technology, a simple and quick sample pre-treatment method is established, wherein the detection limits of the dinotefuran and metabolites, UF and DN, thereof are respectively 0.002 mg/kg, 0.002 mg/kg and 0.01 mg/kg. The method is simple in operation, is quick and accurate, and has high sensitivity and good repeatability.