The invention relates to a durable polyurethane finish capable of resisting marine-atmosphere environment, and a preparation method thereof. An A solution is prepared by an HDI trimer, a corrosion inhibitor and polyurethane-grade butyl acetate; a B solution is prepared by a polyurethane resin hydroxyl component, xylene, a polymethacrylate solution, a fluorine-containing organosilicone solution, a silicone-free acrylic polymer, a polysiloxane-polyether copolymer, a mixture of alkaline and acidic fatty acid surface active substances, a ultraviolet absorber, a light stabilizer, a polyurethane curing accelerator, a polyethylene micronization wax and precipitated barium sulphate, quartz powder, sericite powder and rutile-structured titanium dioxide. When being in use, the A solution and the B solution are mixed and cured to form a coating. The coating has good adhesion with a micaceous iron epoxy coating and an epoxy paste coating and has excellent weather resistance and salt fog resistance. An artificial accelerated aging test shows that gloss retention of the finish can reach 80% at 3,000 h. The finish can be applied in ocean platform overhead pipelines and offshore wharf surface pipelines.