In order to achieve the high-precision measurement of bifacial angle in large- scale space,machine vision is used for the inspection of angle between the commo n reference and target.Firstly,the methodology of bifacial angle measurement in large-scale space is proposed,the line structured light is used as the common r eference on the direction of the projective plane and the method of optical refe rence inspection is proposed.Secondly,the original images of the targets used fo r representing the lines including the angle which is calculated with the image processing technology are designed.Then,the method of self-adaption segmentatio n is discussed in this paper.Meanwhile,edge extraction algorithm and criterion o f target selection with high capacity of resisting disturbance are designed.Fina lly,system measurement accuracy is analyzed.Repeatability precision of space ang le measurement is ±0.0115° while the object distance is 300mm and the intensities of light at the two measuring positions are 182lux and 150lux.Experimental results indicate that the algorithm designed in this paper satisfies the demand of the online measuring system.