In sulfuric acid solution，Fenton reaction was used to produce hydroxyl radical to discolor fast green. But malondialdehyde（MDA） could inhibit the oxidation of hydroxyl radical on fast green. Based on this fact，spectrophotometric method for determination of MDA by color-fading of fast green was proposed. In the optimal experimental conditions, in the linearity range of 0.083μg/mL～3.33μg/mL, the regression equation was △A625nm=0.0837ρ＋0.0204，with correlation coefficient of 0.9926 and detection limit of 0.038μg/mL. For the determination of MDA in foods，this method presented RSD of 1.5%～2.7% and recovery of 96.2%～106.9%.