This paper focuses on the adjustment of B-spline approximation to terrestrial laser scanning (TLS) data and its contribution to deformation analysis of composite arched structures. The deformation of an arch structure under static loading conditions are investigated with TLS technology which is accurate, time-efficient, and capable to obtain dense 3D coordinates of point clouds for the measured objects.Highly accurate approximation methods for the point clouds data are extremely important for structural deformation analysis. The innovation of this paper is that parameters of B-spline is optimized with laser tracker (LT) to improve the accuracy of deformation monitoring and analysis, where the result is justified with LT data and the uncertainties are analyzed. It is revealed that optimized B-spline approximation agrees better with LT result. The improvement to the B-spline curve with minimum standard deviation reaches 52%, and its improvement to polynomial approximation reaches 77%.