The invention discloses an engine correct time angle measuring device and detection method. A lower end of an installation support rack is provided with a base plate, a lower end of a measuring rod of a displacement meter perpendicularly contacts with a top face of a piston, a pointer is fixed at one side of an engine, a tip of the pointer points to a graduation of an angle scale, and the angle scale is mounted on a shaft end of a crankshaft. A graduation of 0 on the angle scale is a piston top dead centre reference point, an installation direction of the displacement meter is adjusted in such a way that the measuring rod of the displacement meter is perpendicular to an air valve spring installation seat, a camshaft is driven to complete one rotation cycle, a maximum life range position of the displacement meter is found, and an angle of the angle scale is read as a correct time maximum angle. The displacement meter perpendicularly contacts with a top part of the piston via a probe, the probe can move up and down along with the piston, a distance that the piston moves can be read via the displacement meter, an angle through which the crankshaft rotates can be read via the pointer, and driving components can be subjected to deviation correction operation according to a deviation value after correct time signal detection is completed.