Study on the forms of inorganic phosphates and their usefulness in black soils in Jilin province by Gu and Jiang's method. The results showed: the amount of inorganic phosphates about 60%~80% in the total-P of black soils,and their composing is:O-P(16.25%~61.0%)>Fe-P(11.42%~38.63%)>Ca_(10)-P(11.66%~34.48%)>Al-P(8.71%~23.77%)>Ca_2-P(5.17%~22.51%)>Ca_8-P(1.81%~27.19%)?Use related coefficient analysis and path coefficient analysis to discuss the relation between every form inorganic phosphates and available phosphates, draw the conclusion that: available phosphates that with draw by Olsen's method mainly is Ca_2-P, their relativity is very obvious, but Al-P,Fe-P are valid complement of Ca_2-P.Every form inorganic phosphates is stable relatively on composing, and they can effect each other. Established the equation between Olsen-P and another factors that effect mainly on Olsen-P.