Abstract: A new method of estimating the influenced areas of the leaked toxic gas in transportation is proposed. The course and features of continuously leakage are discussed with the consideration of both the diffusion process and the movement of the traffic flow. The actual influenced area of the toxic gas on highways in different situations is analyzed and estimated based on Gaussian model. A leakage accident of chlorine happened on Jinghu Highway is taken for instance to illustrate the feasibility and applicability of the proposed method.