The invention belongs to atmospheric infrared detection equipment, and specifically relates to a receiving and transmitting integrated open light path atmospheric detection system. The receiving and transmitting integrated open light path atmospheric detection system comprises an infrared signal transmitting unit, an infrared signal receiving unit and at least two reflection units, wherein the infrared signal transmitting unit and the infrared signal receiving unit are integrated in a machine body; an infrared light beam transmitted by the infrared signal transmitting unit is projected to the reflection units, can be returned back the way to the machine body after being reflected by the reflection units and can be incident to the infrared signal receiving unit; the at least two reflection units are distributed in a detection space zone at intervals; an emergent direction of the infrared light beam is set to be adjustable, so that the infrared light beam can be selectively projected to any one reflection unit. According to the receiving and transmitting integrated open light path atmospheric detection system disclosed by the invention, the stroke of the infrared light beam is doubled by utilizing separated reflection of the reflection units, the distance between two devices under the same stroke is shortened, and the device debugging difficulty is reduced; in the receiving and transmitting integrated open light path atmospheric detection system, the infrared light beam can be switched in several different paths, so that atmospheres in different directions in a to-be-detected zone can be detected, and detection data are more reliable.