Abstract: This talk contains two parts. The first part is to introduce a first-principle approach to statistical physics. First we introduce a basic principle, called the potential-descending principle (PDP). Then we show that PDP, together with the classical principle of equal a priori probabilities (PEP), leads to the first and second laws of thermodynamics, irreversibility, and the three classical statistics: the Maxwell-Boltzmann, the Fermi-Dirac and the Bose-Einstein statistics. Consequently, PDP and PEP are the first principles of statistical physics. Also, PDP leads to the standard model of statistical physics. In the second part, we present a dynamic transition theory for dissipative systems, and in particular for thermodynamic systems. This is joint work with Dr. Tian Ma.