Abstract: In this research, a new definition of reference crop evapotranspiration and Penman-Monteith formula put forward by Food and Agriculture Organization of the United Nations—Irrigation and Drainage Paper 56 published in1998, was used in analyzing the temporal and spatial variation of reference crop evapotranspiration(ET₀) in Shanxi Province. Daily weather data were selectedfrom eleven representative weather stations(from 1991 to 1999). ET₀ calculation was fulfilled with programm using Visual Basic 6.0; original data and calculated result were stored in SQL Server2000 Database; contour analysis was conducted using Arcmap9.0. In addition, the Average Method, month ET₀ couldbe directly obtained by average day ET₀ in the month, was advanced andusedin calculating month ET₀ instead of Penman-Monteith formula. Following the methods used in this research, the isoline maps of corresponding day, month ET₀ can be produced.