7. The method for utterance verification as claimed in claim 3 further comprising: calculating an overall minimum reference score, wherein the overall minimum reference is a summation of the minimum value of log-likelihood scores of the feature vector of each frame conditioned on each state of each of the model vocabularies; calculating a fourth verification score according to the optimal path score, the overall maximum reference score and the overall minimum reference score; and comparing the fourth verification score with a fourth predetermined threshold value, so as to reject or accept the recognized vocabulary.
8. The method for utterance verification as claimed in claim 7 , wherein an equation for calculating the fourth verification score is: CM 3 = ∑ t = 1 T ⁢ optimal s i ∈ w m ⁢ { s 1 , s 2 , … ⁢ , s N m } ⁢ [ log ⁡ ( Pr ⁡ ( o t | s i ) ) ] - ∑ t = 1 T ⁢ min s i ∈ w m , m = 1 , 2 , … ⁢ , M ⁢ { s 1 , s 2 , … ⁢ , s N m } ⁢ [ log ⁡ ( Pr ⁡ ( o t | s i ) ) ] ∑ t = 1 T ⁢ max s i ∈ w m , m = 1 , 2 , … ⁢ , M ⁢ { s 1 , s 2 , … ⁢ , s N m } ⁢ [ log ⁡ ( Pr ⁡ ( o t | s i ) ) ] - ∑ t = 1 T ⁢ min s i ∈ w m , m = 1 , 2 , … ⁢ , M ⁢ { s 1 , s 2 , … ⁢ , s N m } ⁢ [ log ⁡ ( Prob ⁡ ( o t | s i ) ) ] , wherein, t is a frame sequence number of a feature vector in the feature vector sequence, o t is a feature vector of a frame with the sequence number t, T is a total frame number of the feature vectors, s i is one of the states of a model vocabulary m, w m {s 1 , s 2 , . . . , s N m } is a set composed of the states of the model vocabulary m, M is a total number of the model vocabularies, log(Pr(o t |s i )) is a log-likelihood score of the feature vector o t obtained conditioned on the state s i , ∑ t = 1 T ⁢ max s i ∈ w m , m = 1 , 2 , … ⁢ , M ⁢ { s 1 , s 2 , … ⁢ , s N m } ⁢ [ log ⁡ ( Pr ⁡ ( o t | s i ) ) ] is the overall maximum reference score, ∑ t = 1 T ⁢ optimal s i ∈ w m ⁢ { s 1 , s 2 , … ⁢ , s N m } ⁡ [ log ⁡ ( Pr ⁡ ( o t | s i ) ) ] is the optimal path score, and ∑ t = 1 T ⁢ min s i ∈ w m , m = 1 , 2 , … ⁢ , M ⁢ { s 1 , s 2 , … ⁢ , s N m } ⁢ [ log ⁡ ( Prob ⁡ ( o t | s i ) ) ] is the overall minimum reference score.