The complex hydrogeological conditions and unique hydrochemical environment in the seabed rock often cause serious mine water inrush during undersea mining. With the exploitation of the undersea gold mining area in Sanshandao as the research background, a numerical analysis method for the seepage behavior of the surrounding rock in undersea gold mining considering the hydrochemical corrosion was put forward. A numerical simulation analysis of the undersea mining area in Sanshandao was conducted by the established method, and the results showed that mining the submarine ore body significantly changed the seepage field of the surrounding rock around the stope and water levels dropped obviously in the ore-controlling fault zone. Differences in the hydrochemical environment significantly influenced the distribution of the seepage field of the surrounding rock. The calculation results based on three fluids with different pH values show that the head variation range is the largest when pH = 2, followed by pH = 4, and pH = 7 has the smallest head variation range. The water inflow in the stope was also directly affected by the hydrochemical environment. With the change of pH, the water inflow at each boundary of the stope increases exponentially.