Magnesium potassium phosphate cement (MKPC) is usually prepared from dead burned magnesia (MgO) and potassium dihydrogen phosphate (KHPO, KDP). Here, MKPC was produced by mixing KDP and dipotassium hydrogen phosphate trihydrate (KHPO·3HO, DKP) as phosphates. To study the influence of DKP on the hydration process and hardening, pH values, wettability between magnesia and initial solutions, hydration temperature development, initial setting time, fluidity, hydration products, and mechanical properties were measured. The results show that the decrease in the ratio of KDP to DKP leads to an increase in pH and a decrease in wettability, resulting in changes in the hydration process. In addition, setting behavior is also influenced by the ratio of KDP to DKP. When KDP/DKP＞2:1, as the ratio becomes smaller, the initial setting time gets shorter; otherwise, the opposite is true. These differences are attributable to the temperature change during the reaction, the distinction in wettability, and the different pH caused by the various ratios of KDP to DKP. Moreover, XRD analysis shows that the hydrated products are still MgKPO·xHO (x = 1 or 6), indicating that hydration products are basically unaffected. TGA analysis signifies that the amount of hydrated products in MKPC is responsible for the changes in the mechanical properties.