Because the content of impurity in HgCdTe thin film materials has a great influence on the performance of infrared detectors, the requirement for the purity of bromide methanol etching solution used in the substrate surface processing is very high. In this paper, an improved sub-boiling distillation device is used in further purification of high purity bromine solution, and the impurity content is further reduced by optimizing the experimental conditions according to the results of ICP--MS， which is beneficial to improve the performance of HgCdTe infrared focal plane detectors.