The invention discloses a method for detecting the content of homocysteine in blood or urine. The method comprises the following steps: 1, respectively mixing a standard substance and a sample to be tested with an internal standard solution, adding a matrix solution, and uniformly mixing; 2, adding mercaptoethanol, dithiothreitol or TCEP (trichloroethyl phosphate), uniformly mixing, and allowing the obtained solutions to stand for 10min; 3, adding trichloroacetic acid with the mass percentage of 10%, centrifuging at a high speed, taking the obtained supernatants, diluting the supernatants by deionized water, carrying out liquid phase-mass spectrometry by respectively allowing the diluted supernatants and a mobile phase to flow through a chromatographic column, and finally determining the content of the homocysteine in the blood or the urine. The method for detecting the content of the homocysteine in the blood or the urine of the invention has the advantages of simplicity, rapidness and sensitivity, can be applied to the screening of a large amount of samples, and makes accurate quantification and strong specificity be realized.