This paper discussed a method on reconstructing the log figure using the limited number of sampling points, showed the cubic spline function and parabola equation in the form of parametric vector equation, analysed the fitting error between original longitude curve、 sectional curve and fitted longitude curve、sectional curve by using cubic spline function and parabola equation respectively. The results indicated that it was suitable for parabola blending curve to fit the log sectional curve when the number of sampling points was 12, the maximum fitting error was 3.64%, the mean error was 0.93%; for cubic parametric spline curve to fit longitude curve while the sampling points were 5 or 6, the maximum fitting error was less than 5%, the mean fitting error was no more than 1%.