The host port interface（HPI） of a digital signal processor（DSP） is used to realize the communication between dual-CPU in the distributed power quality monitor. The monitor design scheme is based on the dual-CPU structure of an ARM（S3C2410X）and a DSP（TMS320C6713）. The hardware connection structure of the HPI is given. The essential points of programming the HPI driven program in the WinCE operating system are discussed. For the HPI driven program， both the program flow of the interface function named HPI_Init and the setting of registers related to S3C2410X are illustrated. Finally， the factors affecting the HPI communication speed and the HPI communication protocol adopted by the monitor are described.