This study is performed to select irrigation design year from 10-year return period 7-month(April to October) precipitation amount and compare reference crop evapotranspiration at 13 regions by REF -ET model 1. Seven-month growing season average reference crop evapotranspiration values showed low values of 4.1~4.2mm/day by FAO-24 Corrected Penman method. and 3.6~3.7mm/day by FAO-24 Blaney Criddle method in Chinjn and Ulsan, high values of 4.9mm/day by FAO-24 Corrected Penman method, 4.1mm/day by FAO-24 Blaney Criddle method in Mokpo and Pohang. 2. Estimated seven-month growing season average reference crop evapotranspirations are 4.6mm/day by.FAO-24 Corrected Penman method., 3.9mm/day by FAO-24 Blaney Criddle method, 4.0mm/day by 1985 Hargreaves method, respectively.