The goal of this paper is to develop a fast denoising approach (FDA) to infrared (IR) images. The IR images usually have noise, edges, text information and small objects of interest. The well known standard median filter (MF) is not suitable to process these IR images. The main characteristics of the proposed approach are that no prior knowledge about the IR image noise is necessary and no parameters must be preset. It is developed based on IR imaging mechanism to detect the noisy pixels and on modified median-based filter to remove the noisy pixels in IR images. The FSN approach has the advantage of low computation load. The goal of the proposed approach is feasible for an effective process for reducing noise of IR images. It also significantly speeds up the denoising process and can apply to real-time video processing.