Abstract: A new concept—chaos degree of motion field was proposed to accelerate the computation of multi-block mode motion estimation while preserving its high performance of video compression. We deduced correlation model between chaos degree of motion field and optimal block mode by exhaustive statistic observations. A fast mode selection algorithm was proposed according to the correlation model and theoretical analysis. Simulation results on JM72 show that CDMF-FMS(Fast Mode Selection based on Chaos Degree of Motion Field) could reduce 20% of computation time with the same compression performance as the full mode motion estimation.