Abstract: The determination of the minimum sample content is a key question when the stochastic simulation method of microtopography is used to evaluate the effect of the spatial variability of microtopography on the basin irrigation performances. Based on large amount of data from numerical simulation experiment and probability and statistical theory, the relationship between the mean and standard deviations of basin irrigation performances and sample content of stochastically generated surface relative elevation is built, then the minimum sample content of stochastically generated surface relative elevation which is used to reflect the population is determined according to the stable values of the basin irrigation performances. Results show for the same basin type, the minimum sample content is relatively small for better land leveling precision or lower interval estimation precision, and the minimum sample content is very sensitive to the interval estimation precision. The determination of minimum sample content could supply an effective tool for studying the effect of the discrepancy of undulation location corresponding to the same undulation degree on the basin irrigation performances.