Abstract: Solving Helmholtz equations with heterogeneous coefficients can be challenging due to the high-contrast structure and pollution effect. In this talk, we present a novel multiscale method in the spirit of the constraint energy minimization generalized multiscale finite element method (CEM-GMsFEM) by tailoring new trial and test spaces. We establish the inf-sup stability to secure the well-posedness of our multiscale problem and prove the error estimate that is independent of the high-contrast coefficient. The theoretical results are validated by numerical tests, which further show that the multiscale technique can effectively capture pertinent physical phenomena. This work is partially supported by the Hong Kong RGC General Research Fund (Projects: 14305423 and 14305222).