This thesis studies the inter-group variation of the consonant endings among five principal subgroups of the Chaoshan dialect, a branch of the South Min dialect in Eastern Guangdong Province, from the perspective of language contact and horizontal transmission. I conduct a quantitative study to present the synchronic variance of the consonant endings among five Chaoshan subgroups and the diachronic variance from Middle Chinese to modern Chaoshan dialect on a numerical scale. The current literature tends to take the change of the consonant endings as a process of weakening governed by regular rules. My research findings challenge this conventional view. First, the change of the consonant endings from Middle Chinese to five subgroups of modern Chaoshan dialect is irregular, which is an exception to the linguistic laws proposed in the existing literature. Secondly, I find that some characters without consonant endings or with a weakened ending in Chaozhou in the 19th century reverse to have a consonant ending in modern Chaoshan dialect. This reversal contradicts to the weakening hypothesis that regards the change of the consonant endings as a process of simplifying. Finally, my quantitative research shows that Chaozhou dialect in the 19th century in much closer to modern Xiamen dialect than to five subgroups of modern Chaoshan dialect in terms of the relativeness in consonant endings, which is the opposite to the prediction that languages become more and more different and have no consequent contact with other daughter languages after separating from the proto-language. We propose that the actual situation of the consonant endings in different subgroups of the Chaoshan dialect can be better explained from the perspective of language contact and horizontal transmission. The interaction between Han Chinese and non-Han Chinese is the primary reason for the change of the consonant endings of the Chaoshan dialect. Also, the language contact between Chaoshan aborigines and migrants from the Fujian Province leads to the divergence of the consonant endings in different Chaoshan subgroups.Population structure and other social factors determine what phonetic features survive after several times of horizontal transmission.