Two Field experiments were carried out in a farm at El Gharbeia Governorate during winter season 2013 /2014 and summer season 2014 to study the effects of two irrigation water discharge (1.5 and 3 l/s ) and four compost levels ( 0 , 1 , 2 , and 3 ton / fed ) on water use efficiency and yield components of onion and maize crops. The experiments were laid down in split plots design with three replicates. Data show that the increase of irrigation water discharge significantly increased marketable and total yield of onion by 10 .86 and 9. 95 % ,and increased total soluble solids percentage ( T.S.S. %) and dry matter percentage ( D.M. %) by 5.2 and 4.63 % , while decreased significantly culls yield ( Mg / fed ) by 10. 04 %. ,bulb diameter( cm )and bulb weight ( gm ) by5.19 and 5.49 %, for onion crop. The same trend was observed for maize crop. Increasing discharge rates significantly increased by 8.41 , 4.20 , 9.75 and 2.44 % respectively of average diameter, length of ear ,number of rows /ear and grains / row of maize crop. Grain yield affected significantly increased by 9.70 %. Also compost levels effect on yield and yield components in both onion and maize crops. Increasing compost rates significantly increased marketable and total yield. Whereas marketable yield ( Mg/ fed) was obtained by compost 3 ton / fed., the highest by 4.31, 7.60 and 16.19 %. And total yield (Mg / fed) increased by 3.66, 5.89 and 13.26 % compared to 2 , 1 , and 0 ton / fed respectively for onion crop. For maize when increased from 0 to 1 , 2, and 3 ton / fed. Compost levels significantly increased the diameter, length, number of rows / ear and number of grains /row. Grain yield was increased by 4.91, 9.11 and 11.16 % with regard increase compost levels from 0 to 1 and 2 and 3 ton /fed respectively. Moreover the water relation affected by discharge rates and compost levels in both onion and maize crops . Water decreased by 5.71 % due to increase discharge rate and by4.86 ,11.14 and 15.21 % for onion crop. Meanwhile, water decreased by 6.97 %due to increased discharge and by 5.58, 10.55 and 14.79 %due to increase compost levels from 0 to 1 and 2 and 3 ton /fed. for maize crop . Moreover, water use efficiency increase by increasing discharge rates and compost levels for both onion and maize crops. The interactions between discharge rates and compost levels were significant increase for yield components and yield in both onion and maize crops. Interactions between discharges rate 3 l /s and compost level 3 ton / fed. Could be recommended to obtain the best results of onion and maize yield.