In this paper, based on the gas sensitive mechanism of metal oxide semiconductor thin film, the law of gas diffusion, first order aerodynamics and the relative assumption, we present a simple model for the simulation of the steady state gas sensitivity of metal oxide thin film. Our model provides a general mathematical relationship between the steady state sensitivity and the film thickness. The metal oxide semiconductor thin film is supposed to be formed with a finite number of independent layers. Each layer consists of ideally spherical grains with close-packed structure. The target gas is assumed to affect the inner layers either by penetrating through the grain boundaries or by direct interacting with each layer surface. Besides we propose a model to analyze the thickness dependence of the response time for metal oxide gas-sensing film. (C) 2011 Elsevier B.V. All rights reserved.