Abstract: The decomposition of low grade of phosphate-potassium ore in Yaan，Sichuan was carried out by means of phosphoric acid and a kind of additive.Potassium was then dissolved out from the decomposition residue by leaching process of hydrochloric acid.The influence factors of decomposition rate of potassium and silicon were investigated.The optimum reaction conditions were considered to be 2 h of decomposition reaction at 250 ℃，with a 22.23 g of 85% phosphoric acid，the amount of additive was 120% of the theoretical amount，and the volume of hydrochloric acid in leaching process was 95 mL. The potassium decomposition rate can get above 95%，and the silicon decomposition rate can get above 91%.This method laid a certain foundation for the utilization of low grade of phosphate-potassium ore.

Key words: phosphate-potassium ore, phosphoric acid by wet-process, hydrochloric acid, decomposition rate