Abstract: In order to study the driving factors of irrigation water requirement and find the effective measures for relieving the sharp contradiction between the supply and demand of agriculture water resources, in this paper the factors decomposition model for irrigation water requirement was established based on the extended Kaya equation. The logarithmic mean Divisia index (LMDI) decomposition method was used to quantitatively analyze the driving factors for changes in irrigation water requirement. The change of irrigation water requirement was decomposed into 4 driving factors including planting scale effect, planting structure effect, climate change and water saving engineering effect. The irrigating quota of crop and irrigation water utilization coefficient reflected the climate change and water saving engineering, respectively. Two different decomposition methods of LMDI, addition decomposition and multiplication decomposition, were applied to calculate the effect value of the 4 driving factors for irrigation water requirement change. The irrigation water requirement from 1995 to 2012 in Wuwei city, Gansu Province was taken as an example. The effect values of 4 driving factors were calculated in different periods from 1995 to 2012. The results showed that during 1995-2012, the planting structure in Wuwei city was adjusted by reducing the planting area of wheat and increasing planting area of maize and cotton consuming less irrigation water than wheat. The amount of irrigation water requirement in 2012 was decreased by 5.023×108 m3 in Wuwei city than that in 1995 including an increase of 2.435×108 m3 caused by the planting scale effect, and the decrease of 3.994×108 m3, 1.286 ×108 m3, 2.178×108 m3 for the planting structure effect, the climate change effect, and the water saving engineering effect, respectively. The adjustment of planting structure was the most important factor for the decrease of the irrigation water requirement. From the effect value of different crops in the counties of Wuwei city, each crop had different effect on the change in irrigation water requirement. Wheat had the negative impact on the irrigation water requirement change and played a prominent role in decreasing the irrigation water requirement during 1995 to 2012. Among the 4 driving factors for the same crop, for most crops the planting structure effect was stronger than the others in all the regions. In addition, 4 driving factors in different periods played different role in changing irrigation water requirement in the counties of Wuwei city. However, the planting structure always had the inhibitory effect on increasing irrigation water requirement obviously in all the regions and periods except for Liangzhou in 2000-2005.. Water saving engineering had the positive effect on increasing irrigation water requirement in Wuwei city, Liangzhou county and Minqin county during 2005-2012. The main reason was a decrease in irrigation water utilization coefficient. Therefore, improving the efficiency of irrigation water utilization and controlling agricultural development scale are effective measures for saving irrigation water in Wuwei city.