Microwave ablation requires high temperature measurement accuracy to monitor the curative effect of the lesions. PRFS-based MR thermometry is the most commonly used temperature monitoring technique. However, PRFS is hampered by temperature-dependent magnetic susceptibility changes. It has been proved in the Quantitative Susceptibility Mapping(QSM) that susceptibility can be measured from the phase changes ,which is derived from Maxwell’s Equation. In this work, we proposed a practical method to calculate the errors caused by temperature-induced susceptibility changes based on the method in QSM. Both Simulation studies and microwave heating experiments validated the accuracy of the method.