Based on meteorological data of Shenzhen from 1998 to 2007, the paper studied reference crop evapotranspiration by using Hargreaves method, Pristley-Taylor method and Irmark-Allen method with the FAO Penman-Monteith method as the standard, attempt to estimate applicability of the three methods.The results show that mean monthly reference crop evapotranspiration and annual mean reference crop evapotranspiration of Irmark-Allen and Penman-Monteith is no significant difference, but are deviated from Hargreaves method and Pristley-Taylor method which Hargreaves is the most volume and Pristley-Taylor is least.The correlation of Irmark-Allen method, Pristley-Taylor method and Penman-Monteith are overestimated.Irmark-Allen method is advisable to estimate ET0 when hard to get relatively meteorological data in Shenzhen.