A mouth and nose occluded detecting method includes a detecting step and a warning step. The detecting step includes a facial detecting step, an image extracting step and an occluded determining step. In the facial detecting step, an image is captured by an image capturing device, wherein a facial portion image is obtained from the image. In the image extracting step, a mouth portion is extracted from the facial portion image so as to obtain a mouth portion image. In the occluded determining step, the mouth portion image is entered into an occluding convolutional neural network so as to produce a determining result, wherein the determining result is an occluding state or a normal state. In the warning step, a warning is provided according to the determining result.