Abstract: A fast polarity correlation algorithm is presented which utilizes the functions of a standard 8-bit microprocessor to handle 8-bit data and to look up a table. The peak of the correlation function is searched by scanning and bisection method. When it is programmed on a Z8671 Single-chip microcomputer clocked at 7.3728MHz, this algorithm allows a maximum sampling frequence of 18.08kHz, and for a measurement window of 127 points with 256 integrated points, only 10ms is required after collecting data to give out the transit time over distance L. Therefore it is possible to make microprocessor-based correlator for real time applications.