A narrow parallel plates model is used to test and analyze oil migration process in a single fracture. Two glass plates, one side surface of which is rough, are used in the model. The density difference between two phases of fluid is realized by changing the salinity of sugar in water. The experiments were done by changing the fluid density difference and the oil injecting velocity. The results show that the pathways of oil migrating in a narrow fracture is similar to those in a porous medium. The pathways may be reckoned by fractal and occupy only a part of the possible path in the medium. Influenced by different factors, the pathways may be in different modes as follows: piston, finger and strangle. These modes observed in the fracture model may be completely characterized by a migration phase diagram that can be synthesized from experiments of oil migration in a porous medium.