To reduce agricultural water consumption along with presenting an appropriate irrigation planning with conjunctive use of surface water and groundwater resources in agricultural sector, deficit irrigation was implemented on Najafabad sub-basin in the case of four main crops of this region; i.e. wheat, barley, onion and alfalfa. A genetic algorithm was applied in software Matlab to solve the problem. Investigating the effects of applying deficit irrigation on the case study, at first the problem was solved for a scenario of normal condition of water resources and weather parameters. Also, to present a short-time planning for irrigation of the case study, another scenario was defined with considering the parameters of recent 5 years in which the first two years drought condition, in the second two years normal condition and in the last year wet condition was prevailed. At last, the results of the two scenarios accompanied by cropping pattern of each year were presented. Results showed that in the case of the first scenario, water consumption would decline almost 24 MCM; while the net financial return decreased 22 percent. Also, investigating the results, it was concluded that applying deficit levels up to 20 percent would not considerably affect the net financial return of cultivation per hectare. On the other hand, the results of the second scenario showed that in normal and wet conditions decreasing of net revenues would be less than drought condition.