Thermodynamic formula for the spherical droplet was obtained from the different analysis aspect based on the first/second law of thermodynamic. It should be pointed out that the pressure in formula is liquid pressure, but not gas pressure. According to the entropy and Gibbs free energy criteria, it was proved that the vapor-liquid equilibriumcondition is that the chemical potentials of two bulk phase are equal. It is noted that the phase equilibrium condition can not only be applied for the spherical droplet, but also for others shape droplets, and whether it is isolated system or a closed system and the type. In addition, the relevant problems in the literatures were discussed in detail and some obscure opinions were clarified.