How to measure interface tension between water-fluid system is very complex. We can find out that when we measured oil-water system such as benzene-water system or nalkane-water system with known reference value using Wilhelmy plate method or pendant drop method , measured value may be differ from reference value. For Wilhelmy plate method, we find out contact angle of water-fluid system is not 0°, and range of contact angle may be variable from 25-120°. When we use modified Wilhelmy plate method to correct contact angle using Young-Laplace equation, measured IFT value will agree with reference value. But when measuring IFT based on pendant drop method, no contact angle is needed to correct.After serious analysis and compare, we find out we must saturate fluid (benzene or nalkane) with water at first, then measured value will agee with reference value. Please contact http://www.usakino.com to ask how to saturate fluid with water and what is most suitable method to measure interface tension between water-fluid system. we have achieved a most suitable measurement of IFT used drop shape analysis system (contact angle meter model SL200K series)