Abstract: The relative permeability curves to oil and water can exhibit the pore structural variation, oil and water distribution and oil andwater movement and production characters in reservoirs during water flooding. Although there exist various relative permeability curves tooil and water, they can be divided into such five types from actual field data as upward concave, straight line, downward concave, upwardconvex and chair-shaped types to water phase. These types of curves are of contrast shape, obvious feature and different production char-acters. Accordingly, the reservoirs with above relative permeability characteristics can be classified into five types: three pore flow systemswith moderate-high permeability, ow permeability and low permeability and water sensibility, and two fracture flow systems with low per-meability and high conductivity, respectively. It'1l be of an important role to know the relative permeability curves, reveal their reflectedreservoir characters and master the oil and water distribution and movement of different fluid saturations at the beginning of an oilfield development.

Key words: reservoir rock: relative permeability curve, classification, mechanism, feature