With an analytical solution to one-dimensional thermal conduction-convection in soil, the soil thermal diffusivity (k) and liquid water flux density (W) are determined using measured soil temperatures at two different layers. Variations of k and W with time and with the volumetric soil water content are examined for the Naqu site from July 15 to September 15, 1998. Results show that (1) on average, k=0.34*10-6 m2 s-1 and W=1.73*10-5 m3 s-1 m-2; (2) both k and W increase with increasing volumetric soil water content; (3) there is a line relationship between k and W; and (4) on average, the liquid infiltration rate is 2.89*10-5 m s-1.