This study aims to clarify the vaporization propensity of Cs in simulated granular ash through thermal treatment in N-2 atmosphere at 1100-1500 degrees C with the addition of a mixture of CaCl2 and CaO. XRD and XPS were employed to specify Cl-bearing species in the treated ash. The results indicated that CaCl2 addition facilitated the vaporization of Cs. The vaporization ratio of Cs as a function of temperature was nonlinear. The ash melt formed at 1400 degrees C constrained the diffusion of Cs species by blocking the pores and/or decreasing the surface area of the ash particles which, however, was compensated by increasing the temperature to 1500 degrees C. The addition of the mixture of CaCl2 and CaO highly promoted the vaporization of Cs in the ash compared to that of the addition of CaCl2. Formation of wadalite/igumnovite through chemical reactions among granular ash, CaCl2 and CaO, as well as more liquid produced by additional CaO, were in favor of the reaction of Cs with Cl, thereby synergistically promoting the Cs vaporization. Addition of the mixture of CaCl2 and CaO is highly recommended to remove Cs from Cs-contaminated incineration ash during thermal treatment.