A field experiments was conducted during spring season 2015 at the Agricultural field of Veterinary College - Baghdad University. In order to study the effect of irrigation interval in water requirements growth and yield of cowpea by using irrigation scheduling based on applied irrigation water (IW) and accumulative pan evaporation (CPE) which represented empirical pan factor (Ef). Six-irrigation treatment ware chosen (Ef 0.6, Ef 0.8, Ef 1.0, Ef 1.2, Ef 1.4, and Ef 1.6). The results showed that the irrigation interval was variable values and is decreased by increasing Ef value and with the progress of growing season. The 1.2 IW:CPE and 1.0 IW:CPE treatments with approximately 3-4days irrigation interval was achieved the best in subsequent results. The results showed that the total amount of water applied of Cowpea grown during spring season was 254.82mm, as a mean based on IW:CPE ratio. The data showed that there were significant differences in vegetative growth of cowpea crop such as plant height, number of branches per plant, biological yield. Pod length, pod circumference, fresh pods yield weight of loosed and number of seed/pod. The results of the effect of irrigating treatments on cowpea seed yield and its components showed that treatment Ef 1.2 was superior in fresh seed yield by, 5.13 6.88 and 7.33 ton hec-1.