With virtual machine technology, distributed services deployed in multiple cooperative virtual machines, such as multi-tier web services, may reside on one physical machine. This situation requires an efficient inter-domain communication channel, and meanwhile transparency and security should be guaranteed, for diverse existing distributed applications are serving on plenty of machines. In this paper, we have implemented a highly efficient inter-domain communication channel, called SChannel, with full transparency to both user applications and network protocol stack, and security between guest domains on Xen platform. Between two co-resident domains, SChannel establishes a two-way shared memory channel with elastic size, which is set up using static shared memory mechanism, instead of high-cost dynamic shared memory. Furthermore, SChannel avoids one additional copy from the shared data channel on the receiver domain side. In our evaluation using a number of standard benchmarks, SChannel increases the throughput 5 times than standard inter-domain mechanism offered by the hypervisor. Compared with other typical transparent inter-domain communication mechanism, SChannel achieves approximately 44.5% improvement of throughput, and reduces more than 3500 CPU cycles per packet.