Software defined networking(SDN) is a research trend as it decouples the control plane from the data plane. SDN applications are essential since they can be used to make the network simple to manage, flexible, more secure and more powerful. Northbound Interface is the communication interface between the controller and applications, it plays an important role in the process of the research and development of SDN. The state of the art of the programming languages in the SDN Northbound Interface is surveyed in this paper. It first summarizes the research background of the programming languages in the Northbound Interface. By classifying these languages into different categories according to their abstraction, programming model, implementation mechanisms and whether introducing new features, the study analyzes the key characteristic and language structure in each category. Incorporating with application scenarios in SDN, this paper compares the advantages and disadvantages of each language, and at the end discusses the future research trend.