This paper describes a system, called reading contract system, based on the concept of mission-based learning. The system is developed in order to foster children's reading habits and active learning attitudes under the design of mission-based learning. Activities in a reading contract are designed to include the steps of dealing with a contract. During the process, children must take risks to fail and try to develop responsibility for accomplishing the task in limited time. The spirit conforms to the most critical characteristic of mission-based learning. The reading contract system is built on a reading website. In this learning environment, some aids and tools are provided to help children setting and achieving their learning goals on reading. The role of parents and teachers is to assist children facing their tasks and collaborate with them in the learning communities.