The invention relates to a method for reinforcing a vault of a soft soil layer of a city tunnel. The method comprises the steps that a grouting hole is manufactured, a grouting pipe is manufactured, agrouting stopping bottom is manufactured, a grouting stopping plug is manufactured, and single-pipe double-liquid grouting is carried out. The method has the advantages that the soft soil layer of the vault of the shallow-buried city tunnel can be reinforced, the technical defects of a sleeve sealing method and a mold bag method can be effectively overcome, the soft soil layer of the vault of thetunnel can be reinforced, meanwhile, a roadbed can be reinforced, and the shallow-buried tunnel can be guaranteed to pass through the soft loose soil layer safely.