Abstract: In order to analyze the response of potato varities to water decifit and investigate the differences of potato varities in water demand,the potato varieties 'Qingshu 9' and 'Atlantic' were treated under five water treatments by referring to the annual average rainfall in the northwest and the experimental area, which was normal irrigation (A) according to the annual average rainfall in the experimental area, and mild (B), moderate (C), severe (D) and extremely severe (E) by level-adjusting deficit irrigation to study the effects of irrigation amounts on plant growth (plant height, stem diameter, leaf area), biomass and its distribution in organs, leaf relative water content, yield and its component, and water use under drip irrigation condition with rainproof shelter in field. The results showed that compared with deficit irrigation, plant height growth rate and leaf area expansion rate of the two varieties under normal irrigation condition were faster . The growth rate of 'Qingshu 9' was higher than that of 'Atlantic', and it continued to increase during measuring period , whereas the leaf area of 'Atlantic' is 1.72 times larger than that of 'Qingshu 9' on the 71st day after sowing, so its single leaf area is larger than 'Qingshu 9'. During the measured period, the changing trends of organ dry matter of two varieties were not consistent under normal irrigation, the dry matter of all organs of 'Atlantic' increased, whereas the dry matter of stems, leaves and root of 'Qingshu 9' increased in the early period and decreased in the late period, the tuber dry matter increased significantly (P<0.05), the distribution ratio of tuber biomass of 'Qingshu 9' was 57.96%, of which, the 'Atlantic' was 85.96% on the 120th day after sowing, indicated that there was still dry matter maintained in stems and leaves rather than in tubers of 'Qingshu 9' at this period, which implies its maturity was later than 'Atlantic'. The trend of leaf relative water content of two varieties was increased and then decreased under normal irrigation. The number of tuber and yield per plant, yield per hectare, the rate of large tuber of 'Atlantic' were significantly higher (P<0.05) under normal irrigation compared with deficit irrigation, while the large tuber rate of 'Qingshu 9' were significantly higher (P<0.05), and the number of tuber and yield per plant, yield per hectare were significantly lower (P<0.05) under normal irrigation compared with mild irrigation, the yield is 92.49% higher than that of 'Atlantic', its water use efficiency (WUE) and irrigation efficiency (IE) are 152.62 kg/(hm2·mm) and 130.70% respectively. With the increase of water deficit, the inhibition of plant height, stem diameter and leaf area expansion of 'Atlantic' was greater than that of 'Qingshu 9', decrease of leaf relative water content of 'Qingshu 9' was less than that of 'Atlantic'. The accumulation rate and absolute value of biomass of two varieties were reduced, resulting in the yield and large tuber rate were significantly decreased (P<0.05), of which the decreasing range of 'Qingshu 9' was smaller than that of 'Atlantic', under extremely severe deficit irrigation, the dry matter of 'Atlantic' at the 120th day after sowing was even lower than that at the 87th day after sowing. Under mild deficit irrigation, the number of tuber per plant and yield per hectare of 'Qingshu 9' showed compensatory effect, which were 22.79% and 11.71% higher than that under normal irrigation, WUE increased 41.48%, IE increased 60.05% and drought coefficient is 1.12. The results showed that 'Qingshu 9' is more resistant to drought than 'Atlantic', the exuberant aboveground growth of 'Qingshu 9' can be inhibited under mild deficit irrigation, which is conducive to tuber formation and expansion, on the contrary, 'Atlantic' should by supplied with sufficient water during the growth period.