The soybean crop growing consists of vegetative, flowering and grain filling stages which any stage has different sensitivity to water deficit. Main aim of this experiment is determining of most sensitive growing stage to drought stress and estimating of yield reaction coefficient during water shortage period and water use efficiency. Then, an experiment with complete randomized block design by 3 replication and 7 water treatment accomplished for JK cultivar of soybean in spring cultivation. Water deficit treatments at different growing stages consists of: TR, irrigation in whole growing period (Control Treatment), TR1, Irrigation with moisture stress in vegetative stage, TR2, Irrigation with moisture stress in flowering stage, TR3, Irrigation with moisture stress in grain filling stage, TR4, Irrigation with moisture stress in vegetative stage and flowering stage, TR5, Irrigation with moisture stress in vegetative stage and grain filling stage, TR6, Irrigation with moisture stress in flowering stage and grain filling stage. Results shows that flowering stage is most sensitive stage for soybean growing period in Mazandaran Province. In TR1 Treatment, water consumption reduced 28% while 4% reduction of yield was observed. TR1, also has Maximum water use efficiency. Yield response factor (Ky) was 0.87 for the total growth period. The flowering stage of soybean was most sensitive and Maximum WUE is related to the treatment of stress in the vegetative growth stage.