The invention discloses a method for extracting glyphosate from heavy glyphosate stock solution by membrane separation technique. It consists of filtering the mother liquid, removing the solid component of the system, then according to the molecular structure, molecular mass, particle size and electric charge, from the big one to the small one, separating step by step by selecting appropriate hyperfiltration membrane, nanofiltration membrane and reverse osmosis membrane to obtain the effective composition of glyphosate. The invention unitizes the separation, concentration and the purification, and is performed at normal temperature. The barrier separation process is excellent in that it is of no change of phase, avoids the decomposition of glyphosate caused by high enrichment and concentration, effectively improves the product quality and yield rate, greatly reduces the energy consumption, is of consecutive operation, low operation cost, and it is energy-saving, highly effective, environment-friendly, furthermore, it can be operated by combining with routine thickening operating unit or be operated individually and is suitable for industrial continuous production.