Extracting changed areas from different images was an important problem in the field of remote sensing image change detection.To solve this problem,a method based on maximal variance between-class criteria and C-means algorithm was proposed.Changed area extraction was converted into a typical problem of two-category classification and could be solved by employing threshold strategy.The C-means algorithm is used to classify an image into two classes and obtained its best threshold when the variance between-class is maximal.The experimental results show that the method can automatically determine the best image change detection threshold and extract the changed areas quickly and accurately.