Abstract: By the way of system investigation and field control experiment,the quantity dynamics of entrap melon fly male adult and damage ratio to Balsam pear,the economic permission damage ratio were established as 2.85%-3.09%,the relationship model between damage ratio and quantity of entrap melon fly male adult were developed,and the economic threshold of melon fly were established as 5.3-5.8 adult per entrapper during ten days.