Measurement of pathological change in pulley tissue is an important index for trigger finger disease. However, the current measurement process is mostly based on manual estimation which is subjective and time-consuming. We hence propose an automatic method for quantitatively measuring the pathological change of pulley tissue from microscopic images. We first apply the color normalization to normalize all the acquired images. Then we use a three-stepped color segmentation process to extract the areas of diseased tissues. On the other hand, we also apply an active double thresholding scheme to segment the nuclei and extract shape features of nucleus. At last, the ratio of abnormal tissue area and the ratio of abnormal nuclei are calculated as the indices for the evaluation of trigger finger disease. The result showed good correlation between the expert judgments and the measured parameters.