The present invention discloses a detection method for cross-linking degree of a reverse osmosis membrane. According to the method, a non-woven fabric layer of a reverse osmosis membrane is completely stripped, a separation layer and a support layer are remained; the separation layer and the support layer are flatly pasted on a glass substrate, wherein the support layer is positioned on the surface, and the separation layer contacts with the glass substrate; according to the solubility difference between the separation layer and the support layer, a proper volatile organic solvent is selectedto dissolve and remove the support layer; a treatment of vacuum drying is performed to remove the organic solvent in the separation layer; a X-ray photoelectron spectrometer is adopted for carrying out sputtering stripping for the surface of the separation layer; finally mole percentage contents of two elements comprising oxygen and nitrogen are exactly detected, and are substituted into a formula to calculate the cross-linking degree of the reverse osmosis membrane. According to the present invention, the cross-linking degree of the reverse osmosis membrane can be exactly detected; the influence on the detection result due to the polymer-modified layer on the surface of the reverse osmosis membrane is avoided; the method has characteristics of simple sample pretreatment process, low cost, strong operability and easy popularization; the technical blank in exact detection of the cross-linking degree of the reverse osmosis membrane with the surface modification layer is filled.