1. A method for utterance verification adapted to verify a recognized vocabulary, wherein the recognized vocabulary is obtained by performing speech recognition on a feature vector sequence according to an acoustic model and model vocabulary database, wherein the feature vector sequence comprises feature vectors of a plurality of frames, wherein the acoustic model and model vocabulary database comprises a plurality of model vocabularies, wherein each of the model vocabularies comprises a plurality of states, and wherein the method for utterance verification comprises: calculating a maximum reference score for each of the model vocabularies according to a log-likelihood score obtained from speech recognition, wherein the log-likelihood score obtained from speech recognition is calculated by taking a logarithm on a value of a probability of one of the feature vectors of the frames conditioned on one of the states of each model vocabulary, and wherein the maximum reference score is a summation of the maximum value of log-likelihood scores of the feature vector of each frame conditioned on each state of a certain model vocabulary; calculating a first verification score according to an optimal path score output during the speech recognition and the maximum reference score; and comparing the first verification score with a first predetermined threshold value, so as to reject or accept the recognized vocabulary.