Abstract: The microstructure of circumfluence and the characteristic of the mixing intensity on the cross-section of thermally stratified shear flow in curved flumes are studied experimentally.By the experimental investigation of the curved flumes with three different sinuosities of 45°,90° and 180°,the transition of the circumfluent structure on the cross-section from the stable stratification to mixing is explored.The four-circulation patterns of the secondary flow are first detected at the critical condition of the conversion of the stable stratification to mixing Moreover,the differences of three-circulation patterns of the secondary flow between stable stratification and mixing are also first discovered,and the reasons of difference between two situations are investigated In addition,the change process of the mixing intensity along the curved flumes is obtained.