Abstract: The two wave coupling is a fundamental and important photorefractive effect.Till now,many papers have studied the saturation effect of the gain coefficient of the photorefractive crystal.The studies found that the gain coefficient Gvaries with the increasing of the light intensity I,and goes through three stages:cut off,increasing and saturation regime.This paper formulated a set of experessions of materials parameters and presents the measuring principles of materials parameters of photorefractive crystal in intermediate regime,namely increasing regime.The experimental results are in accord with the theoretical analysis.