The invention discloses a special culture substrate for rapes. The special culture substrate comprises a germination substrate, a growth substrate, a flowering period substrate and a pod bearing period substrate, wherein the growth substrate is prepared from the following components in parts by weight: 3-16 parts of earthworm cast, 40-55 parts of biogas residues, 5-16 parts of vermiculite, 25-30 parts of biogas slurry, 5-10 parts of rapeseed cakes, 5-15 parts of an auxiliary fertilizer, 4-8 parts of sugar alcohol and 4-8 parts of chito-oligosaccharide; and the auxiliary fertilizer is prepared from 1.5-5 parts of soybean peptide, 1-1.5 parts of montmorillonite and 0.5-1.0 part of compound microorganisms. The culture substrate disclosed by the invention has strong pertinence, the fertilizer is pertinently applied at each growth period, and the utilization rate of the fertilizer is high; the germination times of the rapes can be accelerated, the germination rate is improved, and the stress resistance of the rapes is improved; meanwhile, a germination period and a period from germination to flowering can also be shortened, and a flowering period and a fruit bearing period are prolonged; and the flowering period substrate and the pod bearing period substrate are applied at the flowering period and the pod bearing period respectively, so that the pollination success rate and the pod bearing rate can be improved, the yield is improved, the quality of the rapes is improved, and the plumpness of rapeseeds is improved.