Abstract: Based on meteorological data of 30-year of 135-sites of inner magnolia, ET₀ was computed with Penman—Monteith formula. Spatiotemporal variation of ET₀ in north arid and cold region has been analyzed. At the same time, relationships between ET₀ and meteorology factors (temperature T, humanity RH, wind speed U and time period N) in different regions and time period have been studied. Different model of ET₀ which is adapt to different condition in north arid and cold region was put farward.