Abstract: The potash fertilizer synthesized using desiliconized slag and potassium carbonate is discussed, as well as the influences of the amount of potassium oxide as main raw material and its heating temperature, holding time and cooling mode and amounts of other oxides added on its crystallizability. The results showed that the potash fertilizer can be synthesized using desiliconized slag and potassium carbonate, and the synthesized potash fertilizer is composed of K-containing crystalline Ca1.917 K0.166SiO4, crystalline Ca2SiO4 and other K-containing amorphous compounds. The factors as above were proved no obvious effects on the crystallizability of the fertilizer.