Due to the advantages of lightweight, high sensitivity, wide pressure range, low cost and scalability, conductive polymer composites (CPCs) based on graphene/polymers with three-dimensional porous structures have been the optimal choice for the wearable and flexible strain sensors. In this article, the sensing mechanisms of the flexible strain sensors were first summarized, including crack propagation, overlapping-disconnection and tunneling effect. Meanwhile, three kinds of construction processes of CPCs with porous structures were introduced, including on the basis of polymer foam, graphene/polymer mixed dispersion and graphene foam, respectively. Furthermore, the sensing performances of the flexible strain sensors with porous structures prepared by the above-mentioned three techniques have been summarized, and the relevant examples of flexible strain sensors with porous structures in human motion monitoring fields were presented. Finally, the challenges and development prospects of porous and flexible strain sensors based on graphene/polymers were prospected.