Abstract: In an vitroI acid medium, phosphate in the sampIe reacts with ammonium moIybdate and stammous chIoride to form a bIue compIex. Micro -amounts of phosphor can be determinated in the agueous phase using gIyceroI as soIubiIizing agent, and its maximaI absorption is at 690nm. The mass concentration range of phosphor is between 0~ 2.5 m per 50mL of soIution, and it is direct ratio to absorbance. The suitabIe conditions of coIor reaction are studied.