To study the reasonable roughness value of a long-distance channel, the roughness for a typical section of the Beijiang Water Transfer Project was inversely calculated using Manning formula based on the prototype observation water level and discharge data from 2011 to 2016. One-dimensional unsteady hydrodynamic model was established to verify the roughness value and its spatial difference between channel sections and temporal variation with performance period was analyzed. The results show that the measured roughness of the section is consistent with that of the straight channel section, the roughness of the straight section of the main channel is from 0. 015 to 0. 016. Correction for the effect of channel curves is from 1. 15 to 1. 50, which is related to the complexity of the curve. The channel roughness increases with the running time, and the annual increase of the equivalent roughness K_s was 18. 54 %.