Marine hydrological information plays a significant role in development and exploration of marine resources. Temperature, salinity and depth are fundamental elements of marine hydrology. Monitoring of marine temperature, salinity and depth data plays an important role in the development and utilization of marine resources. The conductivity temperature depth profiler (CTD) is the main instrument for observing seawater temperature and salinity profiles. By using CTD sensors, parameters such as temperature and conductivity of seawater at different depths can be measured. In recent years, flexible electronic sensors have demonstrated great potential for application due to their excellent stretchability and easy attachment, which not only achieve the sensing performance of traditional rigid sensors to a certain extent, but also compensate for the shortcomings of traditional sensors such as large volume and weight. This review introduces the research progress of flexible ocean CTD sensors in recent years, mainly including the working mechanism and classification, common materials, manufacturing processes of flexible sensors, and analyzes the structure, performance, and application platform of existing flexible ocean CTD sensors. Finally, the development of flexible ocean CTD sensors is prospected.