Abstract: In this study, we propose a joint spectrum sensing scheme for Cognitive Radio Networks (CRNs) based on joint spatial and temporal spectrum sharing under Primary User (PU) inference constraint. Compared with temporal spectrum sharing and spatial spectrum sharing, joint spatial and temporal spectrum sharing can exploit more spectrum holes and thereby improve the throughput of secondary system. In the proposed sensing scheme, the mechanism for deriving spatial spectrum hole is given as MIFTP-JSTS (MIFTP based on joint spatial and temporal sensing). The relationship between the spatial and temporal spectrum sensing is revealed. For CRNs with specific periodical spectrum sensing, tradeoff exists between the performances of spectrum sensing and spectrum sharing. An optimization problem is formulated to optimize the performance of spectrum sharing in CRNs and the optimal sensing duration can be derived. Through simulation results and analysis, advantage regions exist for CRNs based on joint spatial and temporal spectrum sharing.