The anticorrosion property of inhibitor used in water-based cutting fluid was studied by electrochemical method.Taking nonylphenol polyoxyethylene ether phosphate ester as an example, the potential curve and AC impedance spectroscopy of 6061 aluminum alloy in the solution of nonylphenol polyoxyethylene ether phosphate ester were measured to assess the corrosion inhibition to water-based cutting fluid.The results of electrochemical method are the same as results of liquid immersion corrosive test method, so potential curve and AC impedance spectroscopy can be used to assess inhibitors of water-based cutting fluid.Nonylphenol polyoxyethylene ether phosphate ester is a mix-type inhibitor, which can inhibit cathodic and anodic process, and its anticorrosion property is improved with higher concentrations within a certain range.