Super-resolution reconstruction has been widely used in infrared images. A lot of effective super-resolution methods have been presented in recent years. In this paper, a fast and robust super-resolution algorithm based on Maximum a Posteriori (MAP) estimation is proposed to obtain a high resolution image from a set of infrared images, which are obtained by an uncooled infrared detector. A comparison and an analysis are made of the super-resolution reconstruction results by this method, with the variance of regularizations and the number of low resolution infrared images, by direct observation and the value of Power Signal-to-Noise Ratio (PSNR). Simulation results with several real sets of infrared images show the effectiveness and superiority of this method for enhancing resolution of infrared images.