Abstract: Heat transfer equation is a kind of basic mathematical-physical equation.The thermal diffusivity is an important thermal physical parameter for soil.The derivation was presented for the one-dimensional heat tranfer equation by means of Fourier series.With the assumption of wave equation for ground temperature,the analytical solution for the distribution of ground temperature at different depths was presented.Based on the analytical solution of heat transfer equation,the principle of measured soil moisture by means of thermal diffusivity was discussed,and two kinds of methods were forward put to evaluate the soil thermal diffusivity,i.e.,the amplitude method and the phase method.The principle of numerical methods to simulate heat transfer in soil was also discussed.Finally,these methods were verified by examples.