The invention relates to a method for analyzing the flow accelerated corrosion degree of a water vapor system of a supercritical unit. The method comprises the following steps: (1) making a standard color chart, and representing the colloidal iron content by taking the color of residues on each filter membrane as the color of the standard color chart; (2) directly connecting a sampling head with a water sample; (3) mounting the filter membrane, connecting the sampling head with a test point sampling pipe, filtering the water sample, enriching colloidal iron in the water sample, and drying; (4) collecting and testing the color chart of the water sample of the unit on site, emphatically the water sample with a relatively large amount of residues in the color chart, pointedly acquiring scale quantity analysis data of unit maintenance, and building a flow accelerated corrosion degree evaluation set; (5) comparing the color of the residues on the filter membrane with the color chart, quantifying the content of colloidal iron in different water samples, and quantitatively determining the flow accelerated corrosion degree according to the flow accelerated corrosion degree evaluation sample set. Compared with the prior art, the method is relatively high in accuracy, simple, feasible, low in analysis cost and relatively institutive in analysis result.