The invention relates to a preparation method for a cross-linked oil water separating film and belongs to the technical field of film separation technique and environment protection. The preparation method comprises the following steps: dissolving isocyanate, poly (ethylene-vinyl alcohol) and polyethylene glycol in an organic solvent; performing cross-linking reaction, thereby acquiring a casting film solution; scrapping the casting film solution into a primary liquid film on a slab carrier; immediately soaking into a coagulating bath for curing; taking out and soaking into deionized water for soaking for 24 hours; drying, thereby acquiring the cross-linked oil water separating film. According to the preparation method, the polyethylene glycol is grafted onto the poly (ethylene-vinyl alcohol) molecular chain through chemical bond connection; the hydrotropic substance is difficult to run off; the stability of the hydrophily and anti-fouling property of the film is ensured; due to the cross-linking structure of the film, the film has higher mechanical strength, water flux and oil drop reject rate. The preparation method for the cross-linked oil water separating film provided by the invention has the advantages of simple operation and controllable film structure; the prepared film is fit for oily wastewater treatment in various production fields; the prepared film is especially fit for the separation of high-concentration oily wastewater.