The technology of extracting potassium salt from low grade potash feldspar was studied by adopting the process of roasting?leaching?separation, and the decomposition mechanism and leaching kinetics were analyzed. The results showed that the decomposition efficiency of ores is better by adding mixed additive agents. The leaching rate of potassium reaches up to 91.88% under the optimum conditions of Ore:CaCl2:Na2CO3?1:0.5:0.1(?), roasting 4 h at 800℃, leaching 2 h at 80℃, ratio of liquid to solid of 1 mL/g. The CaCl2?Na2CO3 mixed additive could effectively decrease the decomposed temperature of ore. The stage of leaching potassium was controlled by internal diffusion process.