Communication between PC and Modem is common, while communication between single-chip computer and Modem is rare. This article will elaborate serial communication between single-chip computer and GPRS modem. The wide use of serial communication will enable various transmission units to connect as one organically and exchange data and information in safe and reliable manner. However, since signal of each transmission channel is different, the serial port in use should be various. Therefore, in order to realize communication among units, it is necessary to involve serial port conversion among each unit.