OpenFlow-based networks simplify network management and improve network programmability by centralized network control. Existing OpenFlow networks employ packet-granularity mismatched packet buffer management to reduce the switch-controller communication overhead. However, the impact of packet buffer management granularity on network performance has not been well investigated yet. In this paper, we propose a novel design of flow-granularity mismatched packet buffer management model for OpenFlow networks, which outperforms the existing packet-granularity buffer management approaches with less communication overhead between switches and controllers. By designing the flow action pre-processing mechanism, we prevent per-flow packet disorder with less packet drop ratio. We evaluate the performance of the proposed flow-granularity mismatched packet buffer management scheme by building prototypes on both software and hardware switches. Experimental results reveal that our proposed method can effectively reduce the switches-controllers communication overhead, as well as preserve packet order for multi-flow OpenFlow networks.