$alpha$-Fe2O3/SnO2 multi-layer thin films were fabricated by APCVD(Atmosperic Pressure Cehmical Vapour Deposition) and annealed at 40$0^{circ}C$ or 4 h, Diffusion of metal ions at the boundary of $alpha$-Fe2O3 and SnO2 layers was analyzed by SEM. EDS and XRD. The crystallite size of SnO2 was affected by the deposition temperature and time. The gas sensitivity (Rg/Ra) of $alpha$-Fe2O3/SnO2 multi-layer thin film gas sensor for NO gas contents of 100 ppm and 1000ppm was 6 and 14 respectively and the response time was 10 sec, The gas sensitivity of thin film gas sensor was improved by multi-layer process