Most of the existing work about device-to-device (D2D) data offtoading do not simultaneously consider the mobile scenario and the trade-off between the revenue and cost of caching data. In this paper, we consider a more comprehensive and practical scenario of D2D data offloading, and design a mobility-aware incentive mechanism to efficiently select some mobile users to pre-cache the proper contents with the objective of maximizing social welfare by jointly considering mobile users' preference similarity and the social relationship. Simulation results demonstrates that the proposed mechanism outperforms other counterparts. In addition, the proposed mechanism satisfies the nice properties of individual rationality and truthfulness.