A new thermodynamic function is introduced and the curve of the function varying with temperature is simulated by using the experimental data of the enthalpy and Gibbs function changes during the isothermal and isobaric process of low temperature thermodynamic systems. The Nernst equation is obtained directly by extrapolating the experimental simulation results to absolute zero without introducing additional assumptions. It is pointed out that the Nernst equation without additional assumptions should be called the Nernst statement instead of the Nernst theorem, and can be the core content of the statement of the third law of thermodynamics. Moreover, the physical connotations of the Nernst equation are explained more accurately.