Abstract: Based on the biological characters of Monochamus alternatus in the forest area of Yunnan Province, a simple and practical method for measuring field population density of M. alternatus was proposed and applied to the measurement of M. alternatus field population density in the 2007—2008 generation. According to the determination data of the 6 observation plots in Yunnan Province, the generation mortality and average population density of M. alternatus pest per single damaged pine tree was positively related to active temperature (≥10°C) accumulation of each site. The results also showed that M. alternatus tended to take a reproductive tactics with high mortality in the warmer southern forest area, whereas a reproductive tactics with low mortality in the cooler northern forest area. The measurement results pretty well reflected the field population density, periodical mortality and generation mortality of the pest in the forest areas of Yunnan Province. It was proposed that this method could be applied to monitoring the field population dynamics, decision making for control strategy, and to testing the control effect of M. alternatus. The best time to measure the field population density of M. alternatus in Yunnan Province was from August to September of each year.