The invention discloses a tunnel portal water sealing method for shield tunneling under conditions of water abundance and deep burying. The method includes the steps: firstly, processing of elastic sealing brushes, namely processing one or more circles of elastic sealing brushes to be mounted on an original tunnel portal of a shield tunnel, wherein each circle of elastic sealing brushes includes a plurality of elastic sealing brushes in peripheral direction; secondly, mounting of the elastic mounting brush, namely mounting the elastic sealing brushes on the inner side of a tunnel portal steel ring on the original tunnel portal; thirdly, filling of sealing grease, namely filling the sealing grease between upper and lower clamping plates of each elastic sealing brush; fourthly, shield tunneling and injection of water sealing materials, namely adopting a shield tunneling machine for shield tunneling from the original tunnel portal forwardly, and injecting water-swelling water sealing materials between a shield and the inner wall of the tunnel in a shield tunneling process. The tunnel portal water sealing method for shield tunneling under the conditions of water abundance and deep burying has the advantages of simple steps, reasonable design, low input cost, simplicity and convenience in construction, excellent sealing effects, effectiveness in long-time sealing of the tunnel portal and safety and reliability in construction.