This study was to determine the yield performance and to assess the stability of three potato cultivars and four irrigation regimes in six environments by using the AMMI statistical model. This experiment were conducted on the three cultivars of potato (Agria, Satina and Caesar) using four different irrigation regimes (first, after 30 mm evaporation from class A evaporation pan, second, after 30 mm evaporation from class A evaporation pan with spraying by potassium humate, third, after 60 mm evaporation with spraying by potassium humate and fourth, after 60 mm evaporation from class A evaporation pan) in three locations of Ardabil in Northwestern Iran and for two years (2007-2008). Experimental design was split plot with three replications. Potassium humate sprayed (250 mL ha-1) in the three stages of emergence, before tuberization and during tuberization period. Combined analysis of variance showed that there were significant differences between locations, years, irrigation regimes and cultivars and their interaction on tuber yield. The analysis of variance for the AMMI model of tuber yield showed that environments, cultivarsxenvironments interaction and AMMI component 1 were significant. Results showed that Agria and Caesar cultivars had high tuber yield in all sites and for the four different irrigation regimes for two years. Caesar cultivar had the less Slop, S.E., MS-TXL, MS-REG and MS-DEV among other cultivars and was the most stable cultivar. The Agria cultivar has adapted in Alarog, Hassanbarog and Khoshkeroud sites under normal (using irrigation after 30 mm evaporation from class A evaporation pan) and normal with potassium humate conditions, Caesar and Satina cultivars in Alarog, Hassanbarog and Khoshkeroud sites under stress with potassium humate and stress conditions in order to ensure their yield stability and economic profitability.