Due to the effect of complicated actions in the longterm operation of seacrossing tunnels, especially under the corrosion of the sea water, diseases may occur to seacrossing tunnels. If these diseases are not treated timely, the structure and operation safety of the tunnels will be jeopardized. In the paper, the diseases of a seacrossing shieldbored utility tunnel are detected out, the structural stability and operation safety of the tunnel are evaluated, the causes for the diseases are analyzed and corresponding disease treatment measures are proposed. In the end, the disease treatment has achieved satisfactory result. The paper can provide reference for the disease treatment of other underwater shieldbored tunnels. 