Abstract: The relationship of water surface evaporation observed from E₆₀₁ evaporator and the small type of 20 cm evaporation pan was derived from observed data from 1982 to 2003 at Aksu water balance experimental station. The relationships between E₆₀₁ evaporation calculated by conversion coefficient and phreatic water evaporation when phreatic water table was zero, measured at phreatic water evaporation experimental station of Weiganhe river irrigation district was also analyzed, and the conception of phreatic water evaporation demand coefficient was presented. The correlation relationships between phreatic water evaporation coefficient and the mechanical composition of soil was established. The results showed that conversion coefficient between water surface evaporation observed from E₆₀₁ evaporator and the small type of 20 cm evaporation pan was 0.65～0.78, water surface evaporation observed from E₆₀₁ evaporator could not replace the phreatic water evaporation when phreatic water table was zero except for fine sand, and relationship between phreatic water evaporation coefficient and content of powder-clay particle was exponential.