Flexible and wearable sensors have attracted wide attention for their potential applications in human health monitoring, telemedicine and human-machine interface systems. Graphene has some advantages of good electrical conductivity, high flexibility, light weight, high thermal stability and potential mass production, as one of promising ideal candidate materials for flexible and wearable sensors. Consequently, recent efforts are made on the controlled fabrication of graphene materials with designed structures towards application in the next generation of flexible electronics. This review represented recent developmenton the preparation of graphene and their applications in flexible and wearable sensors. The preparation methods of graphene materials with different morphologies were introduced. The preparation strategies, working mechanisms, performance and applications of graphene-based flexible sensors, including strain sensors, pressure sensors, temperature sensors, humidity sensors and other sensors were discussed. The multi-mode graphene-based flexible sensors were introduced. It is indicated that graphene-based flexible sensors possess superior sensitivity and stability, having a great potential for applications in temperature monitoring, speech recognition, pulse, motion and respiratory detection. In addition, the existing challenges and the future development of flexible graphene-based sensors were also given.