The invention discloses a low-complexity decoding method based on a polarization code under a deletion channel, and the method comprises the following steps: step 1, determining a position parameter of each decoding node according to an SC decoding factor graph; step 2, calculating probabilities of different scenes on each node; carrying out permutation and combination according to the number andpositions of deletion errors in the three code words, and the occurrence probability weight of a scene corresponding to the specific deletion pattern is calculated; step 3, arranging the scene occurrence probability weights according to a descending order; obtaining a sequence of occurrence probabilities of scenes on each node; step 4, giving a pruning error probability upper limit on each node, and calculating a respective pruning pattern for each node; and step 5, executing SC decoding, and setting the scene probability corresponding to the pruned pattern to be 0 on each node to obtain a final decoding result. According to the method, the decoding complexity can be effectively reduced; the decoding complexity can be reduced while the decoding performance is controlled, and the applicability is wide.