An ultrasonic concentration detector, comprising: a body (10, 11'), a concentration detection tube (20, 40'), and an ultrasonic transducer sheet; wherein, the body (10, 11') comprises a sealed chamber; the concentration detection tube (20, 40') is horizontally disposed, an opening at a first end of the concentration detection tube (20, 40') is encapsulated by a reflection plate (40, 62'), an opening at a second end of the concentration detection tube (20, 40') is encapsulated by the body (10, 11'), a upper side of the concentration detection tube (20, 40') is provided with an upper through hole, a lower side of the concentration detection tube (20, 40') is provided with a lower through hole, and the upper through hole and the lower through hole are communicated with an interior of the concentration detection tube (20, 40'); in the plane perpendicular to the extending direction of the concentration detection tube (20, 40'), an angle of the upper through hole is an angle between a line connecting a first side of the upper through hole with a center of a cross section of the concentration detection tube (20, 40') and a line connecting a second side of the upper through hole with the center of the cross section of the concentration detection tube (20, 40'); in a plane perpendicular to an extending direction of the concentration detection tube (20, 40'), an angle of the lower through hole is an angle between a line connecting a first side of the lower through hole with the center of the cross section of the concentration detection tube (20, 40') and a line connecting a second side of the lower through hole with the center of the cross section of the concentration detection tube (20, 40'); the angle of the upper through hole is larger than the angle of the lower through hole, wherein the first side of the upper through hole, the second side of the upper through hole, the first side of the lower through hole and the second side of the lower through hole are parallel to the extending direction of the concentration detection tube (20, 40'), and the upper through hole and the lower through hole face to each other; and the ultrasonic transducer sheet is disposed in the sealed chamber at the second end of the concentration detection tube (20, 40') facing to the reflection plate (40, 62'). the body (10, 11') comprises a sealed chamber; the concentration detection tube (20, 40') is horizontally disposed, an opening at a first end of the concentration detection tube (20, 40') is encapsulated by a reflection plate (40, 62'), an opening at a second end of the concentration detection tube (20, 40') is encapsulated by the body (10, 11'), a upper side of the concentration detection tube (20, 40') is provided with an upper through hole, a lower side of the concentration detection tube (20, 40') is provided with a lower through hole, and the upper through hole and the lower through hole are communicated with an interior of the concentration detection tube (20, 40'); in the plane perpendicular to the extending direction of the concentration detection tube (20, 40'), an angle of the upper through hole is an angle between a line connecting a first side of the upper through hole with a center of a cross section of the concentration detection tube (20, 40') and a line connecting a second side of the upper through hole with the center of the cross section of the concentration detection tube (20, 40'); in a plane perpendicular to an extending direction of the concentration detection tube (20, 40'), an angle of the lower through hole is an angle between a line connecting a first side of the lower through hole with the center of the cross section of the concentration detection tube (20, 40') and a line connecting a second side of the lower through hole with the center of the cross section of the concentration detection tube (20, 40'); the angle of the upper through hole is larger than the angle of the lower through hole, wherein the first side of the upper through hole, the second side of the upper through hole, the first side of the lower through hole and the second side of the lower through hole are parallel to the extending direction of the concentration detection tube (20, 40'), and the upper through hole and the lower through hole face to each other; and the ultrasonic transducer sheet is disposed in the sealed chamber at the second end of the concentration detection tube (20, 40') facing to the reflection plate (40, 62').