The present invention provides a detecting device and a detecting method thereof. The detecting device serves to detect defects on the display substrate and comprises: a detecting unit for searching for defects on the display substrate and taking pictures of areas in which the defects are located; and a control unit for comparing and analyzing the pictures sent from the detecting unit to assist the detecting unit to search for the defects on the display substrate, and classifying and counting the pictures of areas in which the defects are located. The detecting device can automatically search for and analyze defects on the display substrate, thereby time for analyzing defects on the display substrate is reduced, and defect analyzing efficiency is improved.