The rate and quantity of heat release during hydration of magnesium potassium phosphate cement (MKPC) containing 0、5%、10%、15%、20% and 25% fly ash respectively were measured at 20℃ via isothermal calorimetry. The effect of fly ash content on the hydration process of MKPC was investigated in terms of the relevant kinetics parameters, as well as the final heat release Q_∞、hydration resistance N and reaction constant K were calculated by the Knudsen and Kondo hydration kinetics formula. The results show that Knudsen and Kondo hydration kinetics formula presented a good applicability for calculation of the final heat release and kinetics parameters of MKPC, with very high relevance fitting. Hydration process of MKPC can be divided into 6 stages, and hydration reaction started from the second stage. At the fourth stage of hydration, MKPC changed from nucleation and crystal growth process to diffusion process directly. The content of reaction components of MgO and KH₂PO₄ decrease with the increasing fly ash content varied from 0~15%,resulting in decrease of hydration heat of MKPC. Fly ash participanted hydration as physical fitter and showed little influence on the hydration process of of MKPC. When the incorporation amount of fly ash content varied from 15% to 25%, an increase of hydration heat was matched and both content N and K for each hydration stage of MKPC presented huge variation due to the decrease of borax content and the pozzolanic effect of fly ash.