This paper did research on composite roughness in compound channels from the asymmetry and symmetry of cross-section morphology.Based on the analysis data from massive flume experiments and the influence on compound channel by channel geometry and relative water depth ratio(hf/Hm),this study developed a formula for composite roughness.From the results,it got that in a certain range,the composite roughness increases along with the increasing ratio of flood-plain width.Furthermore,through comparing the computational results when the cross-section morphology is symmetric with the computational results when the cross-section morphology is asymmetric,this research suggests that the composite roughness under the circumstance of symmetry is larger than that under the circumstance of symmetry.