The invention belongs to the technical field of large-span bridge deformation monitoring, and relates to a prediction and assessment method for measuring the deformation precision of arch ribs of large-span arch bridges by a tilt angle sensor. When the tilt angle sensor is utilized to measure the deformation of an arch rib of a large-span arch bridge, the measurement precision of the arch rib under different deformation conditions is predicted and assessed, and a sensor layout plan satisfying the measurement precision requirements under multiple working conditions is comprehensively selected;and by considering the structure characteristics of the arch rib, a base is set to ensure that the sensors mounted on the arch rib are on a same horizontal plane. According to the method, the deflection deformation of the arch ribs of the large-span arch bridges is researched, and by considering the influences of the fragment errors and the angle measurement errors of the tilt angle sensor when the curves are replaced by straight lines in the deformation of the arch ribs, sensor layout manners satisfying the precision demands of arch rib deflection deformation projects are designed, so that the measurement result precision ranges and the reasonability of the assessment layout manners are predicted. The method for carrying out theoretical analysis in advance has important significance for the final field measurement.