Abstract: For the purpose of testing color difference online in batch dyeing process,this paper first use least-square law to build up a model of concentration-uptake rate and a model of concentration-color difference based on experimental data.And then the model of absorbance-concentration and the model of absorbance-color difference are built by using a known function of uptake rate-absorbance as a medium.In this way,the color-difference can be forecasted by testing dyeing absorbance.The feasibility and validity of this new algorithm have been verified by real examples.