Simulation model of the water tunnel project was used to study the effect of the subsequent driving tunnel on the advanced tunnel of underwater parallel tunnels. The results show that the influence scope is the 1.5D distance from the subsequent tunnel driving face; and that the settlement of the crown is the biggest, but settlement between the parallel tunnels is smaller, that is the settlement is like a hump shape; and that the advanced tunnel sidewall is greatly affected near the subsequent driving tunnel; and that seepage affected scope gradually extends to the subsequent driving tunnel side, seepage flow of the crown and invert is larger than that of the sidewall, seepage flow of the sidewall between the parallel tunnels is larger than that of the outer sidewall.