The invention provides a combined casing type hot air distribution system, and belongs to the technical field of ultra-low concentration methane thermal countercurrent oxidation and low-concentrationenergy recovery. The combined casing type hot air distribution system is characterized in that a main pipe (1) and a plurality of branched pipes (3) which are arranged on the two sides of the main pipe (1) and communicate with the main pipe (1); each section of main pipe (1) comprises a conveying main pipe body (6) and at least one layer of outer main pipe body arranged outside the conveying mainpipe body (6) in a sleeving mode, and the air outlet end of the conveying main pipe body (6) communicates with a conveying main pipe body (6) and an outer main pipe body of the next section of main pipe (1); each section of branched pipe (3) comprises a conveying branched pipe body (10) and at least one layer of outer branched pipe body arranged outside the conveying branched pipe (10) in a sleeving mode. The combined casing type hot air distribution system solves the problem of uneven temperature distribution fundamentally, and the temperature distribution of an oxidation bed in the same cross section is more even.