Abstract: Microtopography was recognized as one of the key variables affecting basin irrigation performances. Less study on the microtopography distribution difference with the same unevenness degree on basin irrigation process and performances was carried out. According to the minimum sample size of stochastically generated surface elevation, the microtopography stochastic modelling procedure was combined with the two-dimensional irrigation simulation model to generate different microtopography distributions for each unevenness degree and simulate the irrigation process under different microtopography distributions with the same unevenness degree. The effects of microtopography distribution with the same unevenness degree on irrigation process and performances were analyzed, and the variability of irrigation process and performances due to the microtopography distribution difference for different unevenness degrees was discussed. The results show that the microtopography distribution difference with the same unevenness degree has an important effect on irrigation process and performances, and with the increase of unevenness degree the effects increase. The variability of irrigation performances due to the distribution difference is weak when the standard deviation of microtopography is less than 3 cm, however, when the standard deviation of microtopography is greater than 3 cm, the variability become strong, and neglecting the effect of microtopography distribution difference with the same unevenness degree may incur large errors when evaluating the irrigation performances.