Software Defined Transport Network（SDTN）controls the network resources and status of the transport network logically and centrally by separating control function and transmission function

which can realize the programmability and automatic control of transport network.It can also build a flexible

open

and intelligent transport network architecture for business applications.In the software-defined transport network architecture

the northbound interface is an important link between the SDTN controller and the upper application.However

there is no unified standard

which has brought difficulties to the development of the SDTN.This paper first discusses the popular northbound interface information model Transport Application Programming Interface（TAPI）.Then we design and implement the TAPI northbound interface in combination with the SDTN coordinate controller to test and verify the effectiveness and interoperability of the TAPI northbound interface information model.Finally

we provide a reference for the selection of the SDTN northbound interface information model.