Cloud is an important part of sky. This paper mainly deals with realistic modeling and rendering of infrared cloudy sky. We propose a novel simulation method consisting of cloud morphological modeling and infrared radiation modeling of scene. First, we develop a point density distribution pattern for simulating the clustered distribution of cloud particles based on cloud’s physical mechanism of formation. After that, cloud depth field is established. According to the relation of cloud’s infrared characteristics to physical height, the emissive is computed. Cloud’s radiation intensity is calculated using the Plank’s law. Finally, an infrared image of cloudy sky is generated by mapping thermal radiation energy of cloud and sky to grey space. Theoretical analysis and simulation results are indicative of the good performance of the proposed method to generate infrared cloudy sky scene with expected sense of reality.