In order to study the law of oil displacement by water in vuggy rock; have produced a single cave filling model, and put forward the concept of dimensionless gravity number on the basis of site materials of oilfields, and determined the physical conditions and simulation models on the basis of analogy theory. By carrying out experiments of oil displacement by water, observed different filling degrees, injection locations, types of filling, replacement efficiency and oil distribution after oil being displaced by water. The investigation reveals that. under the condition of low injection high mining,the gravity differentiation between oil and water is obvious, and replacement efficiency is high, so the saturation degree of remaining oil is low,and recovery rate is high; while under the condition of high injection and high mining,concluded the role of gravity and viscous forces in replacement coefficient by analyzing the dimensionless gravity number obtained in the experiment. When dimensionless gravity number around 0.18 and water injection rate around 40ml/min, the replacement coefficient is high, indicating that the water flooding development effect is good. This has important guiding significance for enhancing recovery in carvernous carbonate reservoir.