1. A facial expression operation method applied in an electronic device, the electronic device comprising a camera device, and a storage device that stores a data table recording a plurality of face image samples of users and a plurality of feature values of the face image samples, the method comprising: capturing images of a user by the camera device; determining whether face area of the user exists in the images according to the face image samples; calculating feature values of the face area when the face area exists in the images; determining a facial expression of the user by comparing the feature values of the face area and the feature values of the face image samples; operating the electronic device to perform a corresponding function according to the facial expression; recognizing a plurality of images stored in the electronic device; and storing the images into one or more collections of images of the user when the images match with the face image samples of the user.