The budding rate was one of the standard to reflect the growth of yeast, but currently the analysis of the yeast growth were mainly through technical and statistical manual microscopy, cannot meet the needs of industrial production for accuracy and efficiency are affected. This paper presented a approach of ellipse fitting method based on concave points detection, according the characteristic that Yeast was usually approximate ellipsoid, by fitted ellipse after found concave points, counted the total number and the budding number of the yeast in the image respectively, then determined the rate of budding yeast. Experimental results show that the approach can detect budding yeast detection rate accurately and effectively.