Abstract: The daily evaporation data of 36 stations in the Sichuan basin form 1980 to 1984 are used in this paper. By calculation the correlation functions (only dependent on the distance between two points) of the evaporation data for four months which represent four seasons respectively, the statistical relationship between the relative interpolation standard errors and the correlation functions is concluded. Also, according to the rule that the relative interpolation standard error is not larger than the observational random error, the rational distance between the evaporation networks in this area can be estimated.