A maintenance method for network connection and a computer system are provided. The method is adapted to a computer system having a real-time clock. The real-time clock is configured to regularly wake up the computer system to check whether a network connection is working normally. In the method, a wake up operation to wake up the computer system is received from a user. It is determined whether a connection time of maintaining the network connection so far from a last time of entering a power saving mode is greater than a counting time for the real-time clock to wake up the computer system. It is tested whether the network connection is working normally when the connection time is greater than the counting time. The counting time of the real-time clock is updated to the connection time when the network connection is working normally.