Two major parties in Taiwan, KMT and DPP, have implemented public opinion survey as the formal mechanism for their candidate selections. The employment of public opinion survey in the process of candidate selection is based on two hypotheses: (1) the usage of opinion survey may narrow down the gap between the ”party will” and the ”public opinion”, (2) the usage of opinion survey may reduce the influence of ”nominal party members”. This paper examines the candidate selection process of DPP in 1998 Legislative Yuan Election, and demonstrates that none of the hypotheses above are true. Moreover, when the public opinion survey was applied for the candidate selection, the most important function of the political party will be shrunk.