Abstract: A new mixing model is presented for taking into account the effect of vapor mixing on tray efficiency under the condition of Partial mixing of liquid, arid mathematical correlations are obtained to predict the tray efficiency of distillation column. The calculated results are in good agreement with that reported by Ashley and Haselden and by Hirotake Katayama et al. The mathematical correlations proposed in this paper are simpler and more convenient to use. For limiting cases, the present mathematical model can be simplified to equations identical with those published in the literature.