In order to improve the scheduling efficiency of the synchronous digital hierarchy(SDH) signal mapped to the optical transport network(OTN) signal in the OTN domain, a new service mapping method SDH over OTN(SoO) model under the packet optical transport network(POTN) system architecture is proposed to carry the SDH service. Under the SoO service mapping model, 4 synchronous transport modules(STM-4) signal is mapped to the low order optical channel data unit (ODU0) through a general frame process and timing transparent transcoding, and then multiplexed to the ODUk transmission signal. Compared with the traditional SDH service mapping OTN signal mode, the SoO model can effectively improve the SDH signal scheduling efficiency, which is 2~8 times that of the traditional mode. The network test method is used to verify the feasibility of the mapping method, and has the advantages of low power consumption, low latency, and flexible scheduling.