In order to get a thorough understanding of starting pressure gradient’s characteristic and influence factor in oil-water phase seepage, the starting pressure gradients of different permeability cores in two-phase seepage during water flooding were experimentally measured in laboratory, according to the experimental phenomenon, resistance effect generating starting pressure in the cores’ hole. The result of research shows: The cores that permeability are below 50×10-3μm2 have larger starting pressure, and they increase rapidly with the decreasing of permeability, the water saturations of cores are higher, the starting pressures are larger; The starting pressure of cores that permeability are above 50×10-3μm2 don’t change much with the permeability changing, and the values of starting pressures are small, which decrease with the water saturations increasing; The resistance effects generating starting pressure are related to rock wettability、capillary pressure、oil and water distribution in microscopic pores、solid-liquid interfacial tension and pore throat radius. For low permeability reservoirs, the cores wettability are larger, the water saturations are higher, the solid-liquid interfacial tensions are larger, the resistance effects of oil-water phase are bigger, the cores’ starting pressure gradients are larger.