The invention discloses a water-rich sand layer advance grouting reinforcing method suitable for a complicated urban environment subway tunnel. The method includes the steps of carrying out the water-rich sand layer section grouting design; distributing monitoring points above a target grouting reinforcing area, wherein the monitoring points are used for monitoring earth surface uplift deformationin the grouting monitoring process; spraying a concrete sealing surface on a tunnel face, preparing an artificial slurry stopping wall, and designing a hole position in the artificial slurry stoppingwall; implementing drilling operation and installing a hole pipe; artificially inducing gushing sand in a drilling design section to form a sand layer hole; conducting grouting through the hole pipein the drilling design section to form a columnar slurry bubble, split slurry vein and compacted sand layer area, and implementing earth surface deformation monitoring after grouting ends; adjusting the artificial gushing sand inducing amount and design grouting amount through the earth surface deformation monitoring data feedback; conducting drilling, artificial gushing sand inducing, grouting and earth surface deformation monitoring work in a next design section after slurry is solidified till drilling and grouting ends to complete the grouting work of all grouting holes.