Water is scarce resource and growing competition for water will reduce its availabilities for irrigation. At the same time, the need to meet the growing demand for food is production using less water. In areas where crops have to be irrigated with limited water resource, saving the amount of water lost by evaporation and deep percolation is important. This study was made to compare the effect of conservation agriculture and conventional tillage on amount of water used, crop coefficient, total crop yield, water productivity and water use efficiency of Cabbage vegetable crops under drip irrigation system. The experiment was conducted in 4 farmer’s plots at Robit by transplanting Cabbage using drip irrigation by dividing each plot to treatments of conservation agriculture (CA) and conventional tillage (CT). The experiment was conducted during the dry season November 2016 to February 2017. The average irrigation water applied on the CT was 385mm/season, which is higher than the water applied in CA treatments which are 318mm/season. Analysis of variance show that there is a significant difference on the amount of water applied between the two water management system (P=0.0076). The average seasonal crop coefficient value of Cabbage was estimated in each growing stage and the values for CA and CT were 0.67and 0.71 in initial stage, 0.89 and 1.02 in development stage, 0.97 and 1.19 in mid stage and finally 0.72 and 0.84 in late stage respectively. In addition, there was significant statistical difference in crop coefficient values for development stage, mid stage and harvesting stage between the two treatments at five percent significant level. The average Cabbage yield obtained during the irrigation season in this experiment was recorded as 21.2 and 22.6 t/ha for CT and CA respectively. But the statistically analysis revealed that there is no significant difference in yield amount on the two treatments (pvalue = 0.323). But irrigation productivity has a significant difference at five percent significant level (P=0.005) between the two treatment. There was also a significant difference for irrigation Efficiency between the two treatments at five percent significant level (P=0.0134). From this study, CA has saved water by 18% from CT by reducing the crop coefficient and has given a 3.2% greater yield than CT through better irrigation productivity and irrigation efficiency.