In Mandarin language speaking, some consonant and vowel pairs are hard to be distinguished and pronounced clearly even for some native speakers. This study investigates the signal distance between consonants compared in pairs from the signal processing point of view to reveal the correlation of signal distance and consonant pronunciation. Some popular speech quality objective measures are innovatively applied to obtain the signal distance. The experimental results show that the confusing pair, /l/-/n/, does have the shortest signal distance compared with other consonants followed by the same vowel and lexical tone. The finding suggests that the signal distance is able to evaluate the confusion degree of certain consonant/vowel pair in a numerical and quantitative way. The signal distance of the other consonant/vowel pairs will be explored in the future work.