Abstract: The gap from the engine rotor blade tip to the open half machine magazine is an important parameter that inspects whether the engine is qualified. And its value is of prime importance to the engine on high efficient and safe operation. Based on stereo vision principle, automatic focus technology, edge detection algorithm, this paper designed a blade tip clearance measurement device used in the process of engine assembling. This device realized the non-contact measurement to aero-engine rip clearance with simple operation and high-accuracy measurement. Experiment result shows that the device accuracy can reach to 20 m.