Abstract: Fine-Granularity-Scalability（FGS） is able to smooth the variation of bandwidth by using flexible bit-plane coding.This paper analyzes the high-delay shortcoming of known FGS rate allocation methods based on sliding window，and proposes an improved method with low delay.According to the difference between adjacent video frames，the proposed algorithm uses small sliding window with inserted frames to reach the effect of known methods’ large sliding window.Experiments show that the method effectively cuts down the delay without reducing too much efficiency of rate allocation.