Software overhead in interconnection network communication has currently become the bottleneck of a cluster system. To reduce it, a user-level communication software UMPS based on real-time OS RTLinux is designed and implemented, which is comfortable with VIA. A new concept of semi-polling driven is presented. With the semi-polling driven mechanism, the interrupts frequency is lowered and the processing performance for short message is significantly ameliorated. By means of the address translation and buffer managing algorithm based on the resource-mapping graph, applications bypass OS and interact with network interface directly using asynchronous DMA. So the overhead and latency in communication are efficiently reduced. Experimental results indicate that the throughputs of UMPS for 64 byte and 1500 byte messages are 394 Mbps and 895 Mbps respectively, and the performance of UMPS surpasses that of other mechanisms.