Present paper deals with the correlation between crystal properties of apatite which include the substitution of PO₄^3- by CO₃^2-, a₀、c₀、Da₀、Dc₀ and the CO₂ index, and the availabiliey of powdered rock phosphate. Phosphate ores taken from 99 main mines in China were studied. Besides, two phosphate ores taken from Ivlotocco and Kora in Soviet Union were used for reference. And 21 phosphate ores were: used irr pat culture experiments to verify the relationship between their crystal structure and the availability to plant growth, and the amount of soluble phosphorus extracted successively for three times by 2% citric acid from raw and purified rack phosphate were determined, another series of purified powdered roc's phosphate were prepared for the determination of the absolute citrate soluble phosphate. The results obtained showed that in the lattice of 101 apatites, CO₂ ranged from 3.62 to 0.04%; a_o from 9.331 to 9.380Å the range of c₀ was very small; Ca_o was 391-2242Å Dc_o, 424-2000Å the range of the CO₂ index was 0.000-0.493. The correlation matrix between the availability of powdered rock phosphate and the crytal parameters of apatite showed that the correlation between the amount of CO₂ and the crystal parameters was most signicant (r=0.999). It gives the illustration of the formation of carbonate-fluorapatite on the basis of the P0₄^3- in fluorapatite being substituted by CO₃^2-,And there was significant negative relationship between CO₂ and a_o, Da₀ and Dc_o. The progressively regression analysis indicates that among all the above-mentinned parameters, Da₀, Dc_o p. X-ray the most important role in the availabitily of powdered rock phosphate to platat growth, i.e. the size of its specific surface area is an appropriate index to evaluate the availability of powdered rock phosphate. When raw rock phosphate was extracted dvrectly by 2% citric acid, the obtained resultes were interfered by accompanied carbonate ingredients, and the impact of calcite was obviously greater than that of dolomite. While the purified rock phosphate were used, the impact of carbonates had been eliminated, and the reliability of correlative coefficient between this parameter and the availability of powdered rock phosphate was raised about to 2 times.