According to the abundant data collected in field and laboratory experiments by the State Collaboration Research Group on Evaporation and Heat Loss from Water Surface since 1976 and a number of historical data observed in hydrological stations in the typical regions in China, the elements influencing evaporation from water surface and the nonlinear interactions between them are determined, new non-diiDensional parameters (w_e、Pv、Pe) and new structure of the formulae are recommended.The constant coefficients in the formulae are determined based on the statistical analysis on measured data.The formulae for calculating daily evaporation and heat loss coefficient from water surface by using the data of regular hydrometeorlogical elements (water temperature;air temperature, vapour pressure;wind speed and atmospheric pressure) have been ubtained.The formulae were tested by I860 group data cullected from buth natural lakes (reservoirs) and thermal polluted water bodies during various seasons in different climace regions of China, and from laboratory experimental data as well.It is shown then the accuracy of these suggested formulae is higher then that of other existing formulae. The paper cuasists of two parts.This is the first part, which includes the main nun-diiiiensional parameters influencing the evaporation from water surface, revision of sensible heat flux and atmospheric saturation state un evaporation, structure of the formulae and their empirical constants.