Abstract: There is obvious rhythmicity in thick reservoirs，therefore，it becomes more difficult in forecasting the development index when interlayer exists in thick reservoirs.The functional relation of layer-to-layer conductivity correction factor is derived based on the fundamental principle of fluid flowing through porous media.It not only quantifies the intrinsic relationship between interlayer parameters and vertical flow capacity of thick reservoir，but also quantifies the influencing law of water flooding recovery factor.The influence of different type and thickness of interlayer on the development index is studied.The findings indicate that the degree and effectiveness of keeping out liquids crossing flow between oil layers for different type barriers are different during zone by zone up-going production，the mudstone is the best，the second is sandy shale in which，the effect of keeping out liquids crossing flow between oil layers is limited by thickness，the last is shaly sand，in which，zone by zone up-going production is already not a applicable development mode，therefore，commingled production is proposed.The research result offers a guideline to correctly understand the influence of interlayer on thick reservoir.

Key words: thick reservoir, interlayer, recovery, layer-to-layer conductivity, zone by zone up-going production