The invention discloses an engine flywheel housing observation window and a barring method. The engine flywheel housing barring observation window comprises a flywheel housing and an observation window body formed in the flywheel housing; a flywheel is formed in the observation window body; the flywheel is connected with the output end of an engine crankshaft; a ring gear is mounted on the flywheel; the circumferential surface of the flywheel is engraved with marks of 0-360 degrees; and the flywheel housing is provided and connected with a pointer pointing to the marks of 0-360 degrees. According to the barring method, the flywheel scales and camshaft end surface air cylinder numbers are combined for judging the operating positions of the engine crankshaft, a camshaft and a piston, a valveclearance, valve timing, fuel injection timing and ignition timing are found out and detected, then adjustment is conducted according to the detection conditions, and barring is completed.