Abstract: The design and installation of zirconium aluminum silicate fiberboard (ZAF) as heat preservation lining in microwave metallurgical reactor is often based on experience, which usually has low heating efficiency and poor heating uniformity. It is difficult to meet the requirements of actual industrial production. In this paper, the dielectric parameters of ZAF in the temperature range of 25-1000 ℃ at 2450 MHz were measured by perturbation method for resonant cavity, and the thermal conductivity in the temperature range of 25-500 ℃ was measured by laser flash method. Based on the numerical simulation technology, the influence of the thickness change of the insulation lining on the reflection loss S11, electric field, temperature field and power loss in the cavity is explored. The results show that the dielectric parameters of ZAF increase significantly after 700 ℃; the thermal conductivity increases linearly with temperature after 100 ℃; the structural parameters of the heat preservation lining have an important influence on the heating efficiency and uniformity of the load. When the heat preservation lining thickness is 60 mm (Mode 3), the heating efficiency of the load in the resonant cavity is the highest, the average temperature is 751. 9 ℃ at 300 s, and the total absorption efficiency is up to 88. 5%.