The invention discloses a 'U'-shaped spectral absorption integrated gas chamber. The 'U'-shaped spectral absorption integrated gas chamber is characterized in that light paths in the 'U'-shaped spectral absorption integrated gas chamber are of 'U'-shaped structures; the 'U'-shaped spectral absorption integrated gas chamber comprises a shell, an incident light collimator, a left reflecting mirror,a right reflecting mirror and an emergent light collimator, and the incident light collimator, the left reflecting mirror, the right reflecting mirror and the emergent light collimator are fixed intothe shell and are distributed to form a rectangle; detection light can be sequentially transmitted through the incident light collimator, the left reflecting mirror, the right reflecting mirror and the emergent light collimator, and detection light paths in the shell are 'U'-shaped. The 'U'-shaped spectral absorption integrated gas chamber has the advantages that the detection light paths are of 'U'-shaped structures, the light paths can be folded by the two reflecting mirrors, and accordingly the optical distance length of the detection light can be effectively prolonged; the 'U'-shaped structures are favorable for guaranteeing the internal detection uniformity of the 'U'-shaped spectral absorption integrated gas chamber, the light path adjusting time can be shortened by the 'U'-shaped structures to a great extent, and the 'U'-shaped spectral absorption integrated gas chamber is high in light path adjusting efficiency; the light paths are good in stability, and the long service life can be guaranteed; the 'U'-shaped spectral absorption integrated gas chamber is small and is compact in structure and low in processing cost.