Abstract: The biological ecological characteristics of Monochamus alternatus were investigated by field observation and indoor rearing in Xichang city,such as the geographical distribution,temporal distribution and the period of development.The results showed that the numbers of M.alternatus decreased with the increase of altitude,but the number difference was not significant because of the small span of longitude and latitude.In terms of temporal distribution,the eclosion began in March and reached its peak in July and August,ended in October.It was determined that the larva had five stages of age.The width of head shell was also determined together with the width of back plate and the length of insect body in each age range,and larvas were observed throughout the year,mainly overwintering at the 3rd and 4th instar.