热力学概率是统计物理学中的一个重要概念，直接和玻耳兹曼熵相联系. 本文分析了理想气体热力学概率计算中容易忽略的因素，即气体所处状态. 它会对计算施加限制条件，以保证其玻耳兹曼熵为广延量；计算了理想气体绝热自由膨胀、等温膨胀和等温等压条件下分子数变化时的热力学概率的改变. 

Thermodynamic probability is an important concept in statistical physics, and relates to the Boltzmann entropy directly. In this paper, factors governing thermodynamic probability are analyzed, which may be neglected in calculation, i.e., the state of ideal gas imposes restrictions, and ensures the Boltzmann entropy an extensive quantity. The thermodynamic probability change of the following processes of ideal gas is calculated, i.e., adiabatic free expansion, isothermal expansion and varying molecular number under isothermal and isobaric conditions.