As a simple, reliable and highly standard way of communication, serial port communication is widely used in industrial automation and electrical equipment controller. The paper presents the way to implement serial port communication of a data collection system. Take Visual C++ programming as example, the key code for MSComm control is presented to implement serial port communications between computer and lower computer. It presents how to create and set up the MSComm control properties. Detailed key code design is discussed from sending perspective and receiving perspective. The communication transfer protocol is designed in details with figure illustration and code examples. The communication handshake protocol is designed in details with process presented to show how the handshake does between computer and lower compute. At the end, the running result for the system is shown. The paper also extends its strategy to long distance communications between computer and lower computer. Two designs are mentioned.