Reactive dyes are generally used for the coloration of cotton fabric. However, hydrolyzed/unfixed dyes are generated and fail to react with fibers, which are responsible for decreasing the colorfastness and creating undesirable color migration among fabrics during washing. So, after dyeing is finished, an effective wash should be carried out to remove additional and unfixed dyes with an effective soap-washing agent. Thus, the soap-washing agent plays a significant role during wash-off and also can avoid undesirable effects such as colorfastness, shade variation, stains, etc. Hence, in this article, a series of cationic soap-washing agents were prepared by copolymerizing N-vinylpyrrolidone with DMAEMA, and the working efficiencies were evaluated. All the samples were washed using different soap-washing agents for 30 minutes under 90? temperatures. It was found that the pH factor greatly influences the unfixed dye removal efficiencies in washing liquors and the concentration of the soap-washing agent. The best washing result for removing unfixed dyes was obtained for V/D5/SDS2 soap-washing agent for 1g/L at pH 7 in liquors. The soap-washing agent effectively removes unfixed dye and can prevent color migration among fabrics during wash-off. The characteristics were analyzed by Data color650 spectrophotometer, UV-visible spectrophotometer, Dry and wet rubbing fastness, and Fourier Transform Infrared Spectroscopy (FTIR).