This paper proposed a novel multi-VP shared buffer named DAMQ-PD with mixed PIO and DMA for descriptor injection on NIC chip to decrease the memory and area requirement of statically allocating buffer among multiple virtual ports (VP). An address queue was used to record the address of every data in the shared buffer. Combining each VP's head pointer and tail pointer, each VP's data can be linked in the shared buffer according to input sequence. By doing so, pipelining reading and writing of the shared buffer can be implemented. A heuristic credit management method was also proposed to distribute credits according to the need of each VP, which can automatically switch descriptor injection method from PIO to DMA or vice versa, thus avoiding block execution of user process when no credit is available. Analyses and simulations show that DAMQ-PD achieves high buffer utilization, pipelining write and read, high message issue rate, thus satisfying the low latency and large capacity performance requirement of descriptor injection on NIC.