This paper aims to study Thai democratic deepening and the constitutional engineering with the analytical concepts of ``power sharing`` and ``accountability`` focusing on the 1997 and 2007 Constitution. With regard to power sharing, the 1997 Constitution had the characteristics of majoritarian principle including a two-party system, strengthening of prime minister and the executive`s power etc. It enhanced significantly the aspects of accountability compared with the previous constitutions. The institutions such as Constitutional Court, Commission on Election, Administration Court, Commission on Human Right, Ombudsman, Commission on Anti-corruption, and the Measure for Anti-money Laundering were established by the 1997 Constitution. However, such empowered accountability system were often abused by the political power groups in the political process. The 2007 Constitution has the characteristics of consensual principle including a multiparty system, proportional representation system, weakened prime minister`s power, balancing of cabinet and parliament`s power, pushing ahead with decentralization. However, the consensual principle of the 2007 Constitution came, in part, from the factional interests. It is similar to the 1997 Constitution in terms of accountability system, which enhanced in law but abused often in practice. One of the critical reasons for the failure of the 1997 and 2007 constitutions to consolidate democratic system was the political game played around the so-called network for the monarchy composed by the military, the civilian bureaucracy, Constitutional Court and the privileged classes. The future of the Thai democratic deepening depends on the constitutional engineering in which the factional interests should be excluded, and the rules of power sharing and accountability which traditionally played around the network for the monarchy should be effectively institutionalized.