The FPGA-based 10/100M Ethernet MAC controller and universal asynchronous serial communication controller are designed and connected on chip in this paper. Such functions as writing data transmitted by the serial interface to the Ethernet controller and sending them to the network, and serially outputting network data received by the Ethernet controller are implemented and interconnection communications between Ethernet and the serial are achieved, possessing great practical values in system test. Modularization design is performed on the whole system with VHDL in this study, whose hardware application is verified on Xilinx Virtex2P XC2VP30 development board. The simulation results prove that the design has reliability, stability and good applications in the data transmission test.