The invention discloses a large-section water-rich sandy stratum shield tunneling synchronous grouting method, in which slurry is synchronously poured into an annular gap between a pipe sheet and an excavated hole body through a synchronous grouting system while a shield tunneling machine performs forward tunneling. By optimizing the construction technology scheme, the preparation of the groutingslurry is regulated, and ground surface rotary jetting grouting construction is cancelled to be changed into a synchronous grouting method in a tunnel, so that the synchronous grouting condensation speed is accelerated, the condensation time is shortened, and the slurry strength is improved. Aiming at a water-rich sandy stratum, gaps of a shield tail building is timely filled with the slurry, so that rock bodies surrounding the pipe sheet are supported, and the problem of too much ground surface settlement quantity is effectively solved. By adding an admixture on the basis of traditional shield synchronous grouting, the synchronous grouting slurry, combining with the engineering geological conditions, is blended again, so that the waterproof ability of the funnel is strengthened, and the stability of consolidation of the water-rich sandy stratum is improved.