In order to mark the fuel filling amount and the position of the landing gear piston rod outer cylinder when the aircraft was in a fully loaded state,two black chromium marking lines were plated on the surface of the landing gear piston rod chromium coating.During the aircraft overhaul process,it was found that due to the presence of a certain thickness of the black chromium marking line,the pressure curve of the piston rod during the stroke pressure test after restoring the black chromium marking line was found to be unqualified.In extreme cases,the black chromium marking can affect the normal operation of the piston rod.A laser marking method for chromium coating replacing traditional black chromium marking technology was studied,and the two marking methods were compared.