In this paper, we demonstrate social bases of major parties in Taiwan, examine how DPP attract more supporters in 2004 presidential election, and discuss party alignment in Taiwan. We argue that the capacity of the KMT and the PFP to attract supporters declined dramatically in 2004 presidential election because they failed to respond the rising of Taiwanese identity. The similarities and differences of social bases among major political parties are also provided. Based on the party's social bases, we also discuss the likelihood that cooperation and competition among major political parties in the 2004 legislative elections. The rising of Taiwanese identity and cooperation and competition between and within Pan-Green and Pan-Blue camps might make national election more competitive. In particular, previous experiences have shown that the Pan-Blue camps will face more difficulties than the Pan-Green Camps in the legislative elections.