Abstract: Using the sex pheromone technology，the flight activity of C．suppressalis males of over-wintering generation and the first generation is studied in this paper．The results show that the flight phase of over-wintering males of Asiatic rice borer happens from 16：00 P．m．to 6：00 a．m of the next day，and their most active phase is from 19：00 to 24：00．Compared with the flight phase of the over-wintering generation males，that of the first generation males is 2 hours later and there is often a second phase which is 1：00～2：00 of the next day．In mass trapping test of small scale，the population density of C．suppressalis males in the margin zone is higher and more variable than that in the central area because of the immigration of males．