Abstarct: Potassium is an essential element for different crops such as corn. Potassium can create water balance in plants and reduce water deficit damages. Potassium increases the resistance of plants to other stresses and yield is increased with increasing photosynthetic capacity. In order to study of the effect of drought stress, different levels of potassium fertilizer and defoliation and detasseling on yield and yield components of corn (Zea mays L. cv 370) an experiment was carried out as factorial baxsed on randomized complete block design (RCBD) with four replications. Potassium fertilizer (K2SO4 resource) levels including (100,200 and 300 kg/ha) as first factor, water stress levels including (full irrigation and irrigation up to ear leaf yellowish) as second factor and defoliation and detasseling including (first: without defoliation and detasseling and second: with defoliation and detasseling) as third factor. Results showed that Interactions between potassium fertilizer and water stress affected total grain number, grain yield, 100 seed weight and grain protein. The most amount was obtained with consumption of potassium fertilizer at rate 300 kg/ha and without water stress in all the treatments except of grain protein. Application of 300 kg/ha potassium and without defoliation and detasseling increased stem diameter, stem dry weight, leaf dry weight, total grain number, Grain yield, biological yield and grain protein. Interaction between full irrigation and without defoliation and detasseling was increased stem diameter, grain yield and 100 seed weight. It was also showed that leaf dry weight, grains number per row, total grain number, grain yield and biological yield were affected by interaction between Potassium, water stress and defoliation and detasseling. Thus according to this results the highest grains yield was obtained with consumption of potassium fertilizer at rate 300 kg/ha that was significant with 100 kg/ha level. The maximum biological yield with consumption of potassium fertilizer at rate 300 kg/ha was obtained.