This study tries to put forward a kind of highly effective evaluation method according to the actuality of synthetic Mandarin. Through evaluating the two Mandarin TTS system of Beijing info-quick Sino-voice speech technique corp., the paper explores MOS (Mean Opinion score) method with a view of practicality. During operating, we defined the five-score rather accurately, and composed a set of testing materials. In addition, we trained the listeners on the basic knowledge of phonetics. The listeners participated in the judgment of speech of each score. Therefore, it increased the consistent understanding among different listeners, and avoided excessively disperse scores of different listeners. Moreover, during testing, the materials of two TTS system were set at random, and it can avoid learning effect for listeners. Besides MOS estimate, we also tried to use rather objective evaluating method. The result of assessment is reasonable.