Digital image correlation method (DIC) can realize non-contact displacement measurement of member by spraying uniform speckle on member surface and taking pictures before and after deformation. Considering the problems of poor recognition effect and low calculation efficiency in deformation measurement of traditional integral pixel algorithm for ancient building painted beams caused by painted pattern uneven gray scale, an Improve-Adaptive Rood Pattern Search (IARPS) method is proposed to calculate the entire pixel displacement. Firstly, the search radius of the first search point is estimated, and an exhaustive search is performed within the radius. Then, Adaptive Rood Pattern Search was introduced to search the whole pixel displacement through small diamond search. By using simulated speckle pattern displacement and the bending test of common regular painted pattern decorative wood beam, IARPS is compared with the coarse-fine search method commonly used in DIC. Through comparative analysis, the results show that IARPS method can effectively overcome the imprecision of local computation in the coarse-fine search method, and the calculation efficiency can be improved by 71.6%, which provides a new method to apply DIC to non-contact deformation measurement of ancient painted beams.