Stressstructure model is used to study the backfilling safety and reinforcement technology of the opencut section of Xiang’an subsea tunnel with differential settlement in soft ground. The study results show that the predicted value of the differential settlement of the opencut tunnel is 80 mm, and the minima safety coefficient is 2.11. Although the structural safety coefficient meets the requirements, the differential settlement may induce cracks, dislocations and water seepage, which has serious effects on the operation function and durability of the tunnel. Countermeasures, including reinforcing the arch feet by largediameter root piles, reinforcing the invert by TSS steel pipe grouting, crack sealing by grouting, and backfilling symmetrically and layer by layer, are proposed. The monitoring results show that the predicted settlement coincides well with the measured settlement, the reinforcement has achieved good effect, and the displacement has been brought under effective control.