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.本發明提供一種從固殺草P鹽酸鹽製造高純度之固殺草P游離酸之結晶的製造方法。提供一種方法,其包含以下步驟:將固殺草P鹽酸鹽溶解於水與選自於甲醇、乙醇、丙醇、或異丙醇之醇的混合溶劑、且水與醇的比率為1:3~1:100之溶劑中,並在添加鹼將其中和之後,將固殺草P游離酸結晶化。
