The invention provides a method for calculating reservoir liquid film thickness based on a real core flow test. The method comprises following steps: step 1. effective seepage capability of a real core is obtained; steps 2. ideal permeability of a capillary model is calculated; step 3. when the film thickness is h, a calculation formula of an effective permeability of the capillary model is established; step 4. a relational expression between the effective permeability and the liquid film thickness is established through studying the relation between the core liquid film thickness h and the effective permeability; and step 5. effective permeability of the capillary model is calculated and the reservoir pore throat liquid film thickness is calculated according to the relational expression between the effective permeability and the liquid film thickness. By use of the method, the thickness of liquid film adsorbed and generated on rock surfaces, after liquid enters the core, can be quantitatively characterized; the method provides entry point for thoroughly analyzing the mechanisms of effective seepage capability of low permeability sandstone oil reservoirs, and lays the foundation of reasonable and effective development for compact oil reservoir.