Based on the idea of financial constitutionalism, public finance budget，comparing with traditional names such as state budget, government budget，public budget，finance budget, and so on , can reveal the legal connotation of budget in institution more accurately. On the legal nature of public finance budget ,legal theory, administration theory and eclecticism of the above are prevalent in international community, and the legal theory should be the best choice . Based on the consideration of the historical and real factors, the legal nature of public finance budget ought to being in should be located to a special kind of laws in China.