In view of the problem of the seepage behavior of fluids in low-permeability media, such as the lining and grouting zone of subsea tunnels, may deviate from Darcy seepage, the Hansbo nonlinear seepage model was employed to describe the seepage behavior within the lining and grouting zone. Analytical solutions for the nonlinear seepage field of a subsea tunnel under dynamic water levels were derived using the complex variable method and the method of images, respectively. Furthermore, an analytical model applicable to different support conditions, such as lining, grouting zone, or no support, was established. The accuracy of the analytical solutions was verified through comparisons with numerical simulation results, other theoretical analytical solutions, and laboratory model test results, and the effects of factors such as the nonlinear parameter, dynamic water levels, and the ratio of grouting zone thickness to lining thickness on the seepage field were analyzed. The results show that as the nonlinear parameter increases, the tunnel water inflow decreases, and the grouting zone sustains greater pore water pressure, thereby reducing the pore water pressure sustained by the lining; under the action of periodic dynamic water levels, both the tunnel water inflow and pore water pressure vary periodically; the grouting zone can attenuate the influence of dynamic water levels on the lining, and as the ratio of grouting zone thickness to lining thickness increases, the tunnel water inflow further decreases and the pore water pressure sustained by the grouting zone increases, thereby reducing the pore water pressure sustained by the lining.