In this paper, the in-situ data of the standard penetration test and cone penetration test in Yuanlin, Changhua are taken as case studies. The geostatistics method is used to build the spatial structures of soil parameters including SPT blow count (N), fines content (FC), saturated soil unit weight (W(subscript t)), cone tip resistance (q(subscript c)) and sleeve friction (f(subscript s)), and to determine the variability of design soil parameters. The analytical results show that the horizontal correlation distances in N, FC, W(subscript t), q(subscript c) and f(subscript s) are 1160 meters, 750 meters, 342 meters, 500 meters and 43 meters, respectively. And the vertical correlation distances in the parameters are 9.1 meters, 5 meters, 4.25 meters, 6 meters and 3.15 meters, respectively, which indicates the vertical variability is higher than the horizontal variability. The coefficient of variability in N, FC, W(subscript t), q(subscript c) and f(subscript s) are 17%, 24%, 2%, 6% and 17% in turn.