The invention relates to a middle barrel suitable for the device to kill mosquitoes and/or flies. The middle barrel comprises an external barrel and an internal barrel, the internal barrel and the external barrel are drived moving with respect to the connecting rod by an actuator arranged to the upper barrel； the internal barrel and the external barrel connect to the actuator respectively with the first drawstring and the second drawstring, the second upper cover of the external barrel provides an opening arranged to avoid the first drawstring. Inducer moves to the rod and mosquitoes and/or flies are pressed under water to be drown due to the up-and down motion of the middle barrel, the killing course do not cause secondary pollution or threat to health.<；Figure 11>；
