Abstract: Internet of Things (IoT) connects hundreds of billions of physical objects, and uses information technologies to monitor and control the physical world. Software platform is the key component of IoT system. The core of IoT software platform is the IoT operating system, which are the tentacles of the platform to the terminal of IoT system. The capability elements of the IoT operating system were presented and important IoT operating systems were compared . Middleware is also the important part of IoT system, which hides the complex details of IoT system and supports rapid development of IoT applications. Three kinds of IoT middleware were classified and their different characteristics were analyzed. Finally, based on the analysis of the challenges of intelligent IoT system, the development trend of intelligent IoT software platform was provided.