Thermal load oozing out through the door is the main aspect of the temperature zone heat loss of continuous diffusion furnace. In this paper, multi-layer gas curtain is designed to seal the furnace door in order to reduce heat loss and ensure furnace temperature to meet requirements in regulation. The unsteady flow is presented to better reflect complex time-varying velocity and temperature of curtain gas. Flow and temperature field of continuous diffusion door with multi-layer air curtain are numerically analyzed by Renault model and experimentally tested. And the influence parameters are tuned and optimized based on the theoretic numerical analysis and experiment results.