The utility model relates to an irrigation aid for ditch irrigation under mulch, which can be used for reducing environmental humidity for facilities and comprises a mulching film on irrigating ditches and a row of arc supports, the arc supports disposed below the mulching film are capable of supporting the mulching film into the shape of a half barrel, and arc shapes of the supports at an initial end, namely a watering end, of each irrigating ditch are larger than those of the supports at the tail end of each irrigating ditch. A film opening at the tail end of the mulching film is pressed by soil when the irrigation aid for ditch irrigation under mulch is applied. The problems of high production and operation costs, unsmooth irrigating, water overflowing and the like in the prior art are solved. The irrigation aid for ditch irrigation under mulch has the advantages of high applicability, low production and operation costs, simple structure and the like.