Abstract The equilibrium height of capillary rise and the energy conversion and conservation in capillary rise are discussed from the point of thermodynamics. A reversible process is designed, and thus the reduced value of Helmholtz free energy, the work done by the system against gravity and external pressure are calculated. The formulas of equilibrium height of capillary rise and Laplace equation of spherical surface are obtained. This method expands the application of thermodynamics in surface phenomena, and is helpful for students to understand the energy source of capillary rise.