Abstract: The attenuation process of transverse velocity in the straight outlet section downstream of a bend was investigated. An empirical equation of dimensionless attenuation length (DAL) was established via dimensional analysis. A series results of numerical experiments were adopted to calibrate this equation, as well as to analyze the impact of all factors and the distribution law of DAL. In addition, results were compared with theoretical predictions. The experiments show that Re and Fr have little effect on DAL. Horizontally, the DAL in concave-bank zone is the largest, followed by that in central zone, and the minimum value is in convex-bank zone. Whereas, vertically its value in near-bottom zone is the largest, followed by that in near-surface zone, and the minimum value is in central zone. The vertical distribution of DAL predicted by a typical theoretical equation is qualitatively in accordance with the experimental result. However, disregarding the impact of transverse slope caused its under-prediction near the bottom. Results show that considerations of the empirical equation in this paper are more comprehensive than those of the theoretical equations, and DAL varies horizontally and vertically. When using hydraulic model to investigate the attenuation process of transverse velocity, the similarity law of resistance should be followed, whereas the similarity law of Fr and Re can be neglected at specific conditions.