In high-speed network environment, it's very important to extract elephant flow timely and accurately for cognizing behavior and law of network. In order to reduce the elephant flow measurement missing rate and overmuch occupation of SRAM, an improved algorithm based on LEAST is proposed. By using LEAST elimination mechanism for discarding the mice flow, the elephant flow can be protected. And Window-Reserve strategy is adopted to ensure the fairness of identifying and measuring elephant flow. Finally, through the comparison between the simulation results and the actual flow data, the result shows that the new algorithm has a higher measurement accuracy and is more practicable, and the elephant flow on the average measurement missing rate is reduced to 0%~0.13%.