The invention discloses a detection method of cordycepic acid content in a cordyceps product. The method comprises the following steps: firstly using the cordyceps product to prepare a solution to be detected through a conventional method, secondly using the solution to be detected to prepare a test solution, detecting the absorbance of the test solution with a microplate reader; using cordycepic acid to prepare 5-7 standard solutions with different concentrations, measuring the absorbance of each standard solution; drawing a standard curve of cordycepic acid by using the concentrations of the standard solutions as abscissa and using the absorbance values as ordinate, establishing a corresponding linear relationship equation between the concentration of cordycepic acid and the absorbance, then substituting the absorbance value of the test solution in the equation to obtain the content of cordycepic acid of the test solution and performing conversion operation to obtain the weight percentage of cordycepic acid in unit mass of the cordyceps product. The invention adopts the simple method and cheap devices to detect the cordycepic acid contents of a great number of cordyceps products simultaneously, the system error and the accidental error are reduced, the detection result is not easy to be affected by the external interference and the method of the invention is applicable to conventional quantitative analysis.