The invention discloses a shading device of an on-board road surface crack detection system based on a cam spatial connecting rod, and automatic shading of the on-board road surface detection system is achieved. The shading device is composed of a base 1, a rod base 2, a bearing seat 3, a cover plate 4, a cover plate clamp 5, a pull rod 6, the connecting rod 7, a push rod 8, a cam 9, a motor 10, a cover plate shaft 11, a camera seat 12, a camera 13, a pull rod axle 14 and a cover plate shaft sleeve 15. The shading device of the on-board road surface crack detection system based on the cam spatial connecting rod is simple in structure, easy and convenient to operate, easy to install, low in cost and reliable in performance.