The invention belongs to a cotton linter detection method, in particular to a content detection method of synthetic fiber in cotton linters, which comprises the following steps of: (1) weighing a certain amount of cotton linters, and adding an oxidizing agent into the cotton linters; (2) taking out the cotton linters, and placing in a Capron bag for drip washing; (3) taking out the cotton linters from the Capron bag, transferring to a centrifuge tube for dewatering, and placing the cotton linters in a glass bottle filled with a copper ammonia solution; (4) flushing synthetic fiber into a core funnel by using a washing bottle filled with deionized water, and sucking and filtering solution and moisture by using a vacuum pump; and (5) drying the synthetic fiber in a drying oven, and comparing with the amount of cotton linters primarily added in step (1) to obtain the synthetic fiber content ratio. The invention has the advantages of creating a method which can be used for rapidly and accurately detecting the synthetic fiber content in the cotton linters based on the properties of the cotton linters and the synthetic fiber and the characteristics of various solvents, so that a strict standard can be maintained for comprehensively and accurately assessing the quality of the cotton linter raw material, and a production process is formulated.