在热力学中， 热力学函数，或称 热力学参数、状态函数，是描述热力学系统的宏观物理量。处于平衡态的热力学系统，各宏观物理量具有确定的值，并且这些物理量仅由系统所处的状态所决定，与达到平衡态的过程无关，所以也被称之为状态函数。其中包含了“ 热力学势”，“ 热力学势”特指下面提到的四个具有能量量纲的热力学函数。

热力学系统的状态函数一般存在一定的相互依存关系。如理想气体的状态方程序中，可以任意选取其中的两个状态函数为独立变量，而把其他的统计量看作它们的函数。热力学函数之间的依存关系具有普适性。

In thermodynamics, a state function, function of state, state quantity, or state variable is a property of a system that depends only on the current, equilibrium state of the system. State functions thus do not depend on the path by which the system arrived at its present state. A state function describes the equilibrium state of a system. For example, internal energy, enthalpy, and entropy are state quantities because they describe quantitatively an equilibrium state of a thermodynamic system, irrespective of how the system arrived in that state.