The invention discloses a method for determining the content of vitamin C in forage. By means of a voltammetric polarographic method, the method for determining the content of the vitamin C in the forage comprises the following steps: (1) preparing a sample to be tested, namely the forage which contains the vitamin C into a solution through acetic acid buffered solution with a potential hydrogen (pH) value of 3-5, extracting the solution with ultrasound and obtaining a sample solution to be tested; (2) determining the concentration of the vitamin C in the sample solution to be tested by means of a standard addition method, conducting potential scan on the sample and the samples added through the standard method, taking below 0.2 volt as an initial potential and 0.3 volt as a terminal potential, and drawing a polarographic figure (namely, I-U curve) of each solution and recording a polarographic wave crest current value; and drawing a working curve, and obtaining the concentration of the vitamin C in the sample to be tested directly by means of an extrapolation method. The method for determining the content of the vitamin C in the forage has the advantages of being good in reproducibility and accuracy, low in detection limit, and capable of providing a brand-new method for the trace amount of the vitamin C in the forage to be determined.