A network device includes a timing module, a traffic analysis module, a counting module, a mode switching module and at least one processor. The timing module sets a plurality of continual timing periods each including a plurality of timing periods. The traffic analysis module analyzes if the traffic transmitted by the network device in each of the timing periods in a continual timing period is less than a predetermined traffic threshold, and defining a first analysis result every time that the traffic transmitted through the network device in each of the timing periods in the continual timing period is less than the predetermined traffic threshold. The counting module counts an amount of the first analysis results, and determines if the counted amount is less than a predetermined threshold. The mode switching module switches the working mode of the network device according to the determination of the counting module.