The present invention provides a method for producing crystalline glufosinate P free acid with high purity from glufosinate P hydrochloride salt. In addition, the present invention also provides a method comprises a process of: dissolving glufosinate P hydrochloride salt in a solvent which is a mixed solvent of water and an alcohol(s) selected from the group of methanol, ethanol, propyl alcohol and isopropyl alcohol, and a ratio of water to the alcohol(s) is from 1:3 to 1:100 by volume; crystallizing glufosinate P free acid after neutralizing by addition of a base.