Party politics is an important issue to explain the constitutional work and consolidation of a democracy, and especially for newly democracies. If the party system would be affected by different types of constitutional systems and historical legacy, the party system should also be changed. We have three hypotheses: first, we suppose those countries with a directly elected president will have a higher probability for party system change. And the smaller parties are more likely out of parliament. Second, based on the coattail effect, countries with the concurrent election or the honeymoon election will have a higher probability for party system change. Third, the degree of democratization will also be an important variable in measuring party system change. The party system change will have a higher probability in new democracies, such as in Central and Eastern Europe. Therefore, this paper goes to show that among these three hypotheses, directly elected president and electoral timing are institutional variables, while the degree of democratization is historical legacy.