A Saccharomyces cerevisiae could be acclimated and evolved by a long continuous and close circulation fermentation in the PDMS membrane bioreactor system which coupled the fermentation with pervaporation,and a superior mutant strain could be obtained.In this work,Angel yeast(ADY) was taken as the parent strain and underwent a continuous and close circulation fermentation of 500 h.At termination of the fermentation,as a descendant of 200 generations of ADY,a preferable strain was screened from the residual broth by a usual method.The screened strain was transferred and inoculated into next fermentation and the same screening was conducted as previous fermentation.The fermentation-screening-transfer procedure was repeated three times until a 600-generation descendant was screened.The strain S33 from the third run was showing great superiority over ADY under a substrate prepared by the residual broth after 500 h fermentation,with the cell growth rate,ethanol yield rate and glucose conversion percent increased by 71.8%,53.6% and 52.7% respectively.