The utility model provides a measure dust concentration's optical devices, including the illumination light path, light path and dusty airflow passageway are collected to the scattered light, on the lighting light path, on light source emission beam direction, collimating lens has set gradually, cylindrical lens, photaesthesia district and optical trap ware, on the scattered light collecting light path, the concave surface speculum in proper order, photaesthesia district and photoelectric detector, the optical trap ware includes the barrel, back lid and circular cone reflector, cylinder cavity comprises toper inner chamber A and cylindrical inner chamber B, back lid inner chamber comprises cylindrical inner chamber C and toper inner chamber D, cylindrical inner chamber C and intercommunication adjacent with cylindrical inner chamber B, cylindrical inner chamber C's diameter is 2.5 times of cylindrical inner chamber B diameter, circular cone reflector dress is at toper inner chamber D's osculum end, inner chamber A, inner chamber B, all scribble extinction black paint layer on inner chamber C and inner chamber D's the inner wall and the outer wall of circular cone reflector. The utility model discloses possess the light of blocking simultaneously and eliminate miscellaneous astigmatic function to improve measuring sensitivity greatly.