Abstract: Comprehensive utilization of red mud is significant to environmental improvement and resource recycling.Modification of red mud is favorable to its comprehensive utilization.The degree of mixedness of red mud and limestone directly impacts on modification effect of red mud.In order to determine the degree of mixedness fastly and accurately,extracting conditions of titanium dioxide with hydrochloric acid in the mixture of red mud and limestone were studied.Content of titanium dioxide in extracting solution obtained under the optimal conditions was determined by spectrophotometry,from which the mass fraction of titanium dioxide in the mixture was obtained.And then the degree of mixedness can be measured based on the mass fraction of titanium dioxide in mixture.Research results showed that precision and accuracy of this method are both satisfactory and relative errors are within±2%.It is a simple,rapid,and accurate method and can be used as real-time monitoring of production. 