The invention relates to a modified asphalt for a bituminous concrete closed waterproof layer of a high speed railway, wherein the modified asphalt comprises the raw materials of 60-80 wt% of pavementpetroleum asphalt, 5-32 wt% of a vulcanized rubber powder masterbatch, 1-12 wt% of a butadiene styrene block copolymer, and 0.2-3 wt% of a crosslinking agent according to the weight of the modified asphalt, wherein the vulcanized rubber powder masterbatch is prepared from the following raw materials of the components: 40-80 wt% of matrix asphalt, 10-50 wt% of vulcanized rubber powder and 5-15 wt%of a deconstruction agent. The invention further relates to a preparation method of the modified asphalt and application of the butadiene styrene block copolymer and the vulcanized rubber powder, particularly the combination of the vulcanized rubber powder masterbatch, to the preparation of the modified asphalt, particularly the modified asphalt for the bituminous concrete closed waterproof layerof the high speed railway.