In the early decades of computer age, the most important characteristic of a computer system was its speed. Thus, computers were usually judged by how fast they could perform a given task, and techniques were developed to predict it. Now with the acceleration of social information, not only does users of computers increase, but also the connect area and scale of computer network has increased. Referring to transportation network reliability problem, five new computer network reliability definitions are proposed and discussed. They are computer network connectivity reliability, computer network time reliability, computer network capacity reliability, computer network behavior reliability and computer network potential reliability. Finally strategies are suggested to enhance network reliability.