Spatial working memory is a short-term system for the temporary holding and manipulation of spatial information. Evidence shows that the hippocampus (HPC) and prefrontal cortex (PFC) play important roles in spatial working memory. Though the communication between HPC and PFC is recognized as essential for successful execution of spatial working memory tasks, the directional information transmission in the HPC-PFC network is largely unclear. Therefore, in the present study, neuronal activity was recorded from rat ventral hippocampus (vHPC) and medial prefrontal cortex (mPFC) while the rats performed a spatial working memory task in Y-maze. Then the causality connectivity among the spikes from recorded neurons was estimated using the maximum likelihood estimation and the information flow in the vHPC-mPFC network was calculated to investigate the functional dynamics of the vHPC-mPFC information transmission. Our results showed the increased bidirectional information flow in the vHPC-mPFC network during the spatial working memory task. Both directions of information flow were observed only on trials in which the animal subsequently made the correct response, indicating that the increase in information flow predicted memory accuracy. Furthermore, the information flow from vHPC to mPFC was remarkably higher and preceded that from mPFC to vHPC. These findings suggest that the direct vHPC-mPFC information transmission may be predominant for spatial working memory in rat.