In a method for detecting facial expressions of a portrait photo by an image capturing electronic device, a face captured in the portrait photo is detected. The position and range of the opened and closed facial features are detected, and the facial features within an identified range are magnified according to a specific proportion. A patch of facial features and their surroundings within a specific range is cut according to the magnified identified range, so that the patch can show a change of facial expressions and a specific range of their surroundings. A facial feature classifier is trained by a specific number of opened and closed facial feature samples based on the Adaboost algorithm and used for detecting the facial features in the patch to determine whether the facial feature is situated at an opened state or a closed state.