Abstract: A grid form of inner cover in a bell-type annealing furnace was put forward to resolve the problem about low vertical stiffness of traditional ones. The heat transfer efficiency of the inner cover was compared with traditional ones' via theoretical calculation of influencing factors on heat transfer efficiency such as convection heat exchange coefficient and heat transfer area. It was proved that the grid inner cover could improve the heat transfer efficiency and throughput of the bell-type annealing furnace.