The equation of one-dimensional thermal conduction and convection in soil is solved analytically by applying the traditional harmonic method (HM) and the Laplace transform method (LTM). A simple method to determine accurate values of soil heat diffusivity and liquid water flux density is given. Using this method, we determined the soil thermal diffusivity,k= 0.85 × 10−6m2s−1, and liquid water flux density,W= 4.3 × 10−6m3s−1m−2, for the Naqu site in the summer of 1998. An experimental evaluation of the proposed methods is also given.