Abstract: A device and a method for transmitting data traffic in an OTN are disclosed. First, all the time slots in the payload area of an OTN frame are allocated to sub-domains with certain bandwidth; then, the sub-domains are grouped into sub-domain groups to carry data traffic based on the bandwidth demand of various data traffic. The device and method provided in the present invention map the data directly on the OTN frame after encapsulating the data traffic so as to effectively avoid the redundant overhead and processing in the intermediate network hierarchies; and the bandwidth utilization is increased as much as possible by means of sub-domain and bandwidth allocation in the payload area of the OTN frame.