Two field experiments were carried out for two summer seasons of 2010 and 2011 at Mallaway water Requirements Research station – El- Minia province Middle Egypt . The farm situated at 27ْ 9^- latitude and 30ْ 5^- longitude . Its altitude is about 44 m above mean sea level  . The present research  was carried out to study the effect of irrigation regime and plant population on actual water requirements, water use efficiency , crop coefficient , water saving , yield and economic evaluation for corn crop (20-30 single Hybrid ) . On the other hand , this study aims to evaluate and to compare the potential evapotranspiration (ETP) equations and actual water requirements under El- Minia Governorate conditions  , Also this study aims to observe the effect of  water stress on the yield of corn crop to determine their optnum needs, and produce the highest yield with least possible amount of water  The experiment include five treatments of  irrigation regime and three   levels of  plant population . The   irrigation regime   treatments ( A)  were used as a₁ (control  ) traditional normal irrigation by farmer practices for all stages , a₂= irrigation at 90% of field capacity for all stages , a ₃= skipping 3^rd irrigation at age ( elongation stage ) , a ₄= skipping 5^th  irrigation at age (flowering) stage , a₅= skipping 7^thirrigation at milk (ripeining) stage . While the population densities were b₁ = 18,000  plants / fed ( 30 cm between hills ) , b ₂ = 24,000 plants / fed ( 25 cm between hills ) , b ₃= 30.000 plants / fed ( 20 cm between hills ) . The  treatments of irrigation regime  were assigned to main plots . While , plant population were allocated in sub – plots . So that the experiment was arranged in a split –plot design . The results indicated that the irrigation at 90% of field capacity for all growth stages gave the highest value of the grain yield in the two seasons 27.60 ardab per feddan . while the lowest mean values were 19.100 ardab per feddan was , obtained when skipping 5^th irrigation at flowering stage (A₄) in the two seasons . Also , results indicated the total yield of corn crop increase by about 7.11% and 18.80 % under third population densities (b₃) compared to b₁ and b₂ respectively . Results also indicate that irrigation regime  A₂ ( irrigation at 90% of field capacity for all stages) we cane save irrigation water by about 420.78 m3/fed. (11.28%) under El-Minia conditions , compared with the conventional irrigation by the farmers. The results show also that the mean values of seasonal water consumptive use were 58.18 , 53.19 , 49.64, 49.50 and 49.05 cm/season for A₁, A₂ , A₃ , A₄,  and A₅ respectively . The average values of potential evapotranspiration ( ET_p) by modified Blany & Criddle was nearest  to general average values ( + 3.61%) while , the  farthest values to general average were obtained by  motifed Blaney and Pan evaporation method(-7.39and+5.88%), respectively  (- 7.39 and +5.88 % ) , respectively . Monthly potential evapotraspiration ( ET_p) for Minia , province , Middle Egypt , was calculated using the modified Penman , modified Blaney & Criddle and pan method . Average evaporation values of crop coefficient (Kc ) calculated by many empirical formula for different treatments A₁ , A₂, A₃ , A₄ and A₅ were  0.56 , 0.50 , 0.46 , 0.47 and 0.48  respectively under first population density (b₁)  . While these values , were 0.71, 0.63 , 0.57 , .60 and 0.63 .  respectively under second population density (b₂) and  0.82 , 0.73 , 0.73 , 0.74 and 0.76 respectively  under third population density (b₃). It could be noticed that the nearest values to average Kc which calculated by modified  Blaney & Criddle while the farthest were by  panevapration  method.  In general it can be concluded that modified Blaney & Criddle nearest to actual water consumptive use followed by the modified pan evaporation method so we can recommend this equation ( Modified Blaney & Criddle) for estimating ET_P in Minia region with the average crop coefficient due to the highest accruing for corn crop .