Abstract: Experiments to determination the vertical diffusion in the thermally stratified shear flows in open-channel are described in this paper.The mixing intensity and the interfacial vertical thermal diffusion coefficient near the outlet are analyzed based on the experimental data.The results indicate that apparent difference exists among the running modes of the mixed intensity according to the different fluid states and the different relative positions,the vertical thermal diffusion coefficient is proportional to the mixed intensity and exponential to the outflow densimetric Froude number.The experimental formula is put forward about vertical thermal diffusion coefficient,the mixed intensity and the outflow densimetric Froude number.