In the presence of the increasing demand, it is urgent for the wavelength division multiplexing (WDM) optical transport network not only to boost the transmission capacity but also to enhance the survivability. In this paper, A M:N protection scheme for WDM optical transport networks is proposed and demonstrated. The M protection channels are used to transmit low priority traffic in normal condition, and can be switched automatically to replace a working channel when failure occurs to that working channel. Compared with the 1 + 1 protection system, the proposed scheme achieves better performance with lower costs. An optical add/drop multiplexer (OADM) is also proposed with the protection scheme. Any channel in M or in N can be dropped in the OADM according to the demand of the network management center. When failures occurred to a working channel that should be dropped in the OADM, and when the traffic on the failed working channel has already been switched to a protection channel at the previous node, the protection channel is dropped in the OADM automatically instead of the failed working channel. Then the corresponded adding signal is still added to the working channel, i.e., the protection channel is set free and can be used to carry low priority traffic again to the next node. Experimental result shows that the protection takes place within 7 ms, which satisfies the requirement of the ITU-T recommendations.