The utility model relates to an in-situ detecting device of breakage rate of a metal surface coating in an atmospheric environment, comprising a standard plate (6) which is made of the same material with base metal of a coating to be detected, and a detecting probe, wherein the detecting probe comprises a pallet (1), a silver pole plate (2), a shielding wire (3), a rubber sealing ring (4) and a water-absorbing material (5); the upper edge of the side wall of the pallet (1) is provided with a groove which is internally embedded with the rubber sealing ring (4); the silver pole plate (2) is attached on the bottom surface of the pallet (1), and the shielding wire (3) is welded at one side where the silver pole plate (2) and the bottom surface of the pallet are attached, and penetrates out of the pallet (1) through an opening hole in the side wall of the pallet to be connected with a conductivity meter; the side of the silver pole plate (2), which is not welded with the shielding wire (3) is a working surface; and the water-absorbing material (5) fully dipped with seawater or electrolyte covers the working surface of the silver pole plate (2), and the upper surface thereof projects out of the upper edge of the side wall of the pallet (1). The in-situ detecting device has low cost and simple use method, and can fast detect the breakage rate of the surface coating of a metal structure in the atmospheric environment in situ.