This study is based on the first-principles method to comparatively study the electronic structure and optical properties of tungstate TMWO₄ （TM=Zn， Cd， Hg）. The research results show that ZnWO₄， CdWO₄ and HgWO₄ are all direct band gap materials， and the band gap widths are 2.579， 2.081 and 2.538 eV. The top of the valence band of the three compounds is mainly contributed by the O-2p state. Due to the hybridization effect， the O-2p state and the W-5d state form the bottom of the conduction band together. Analysis of the bond population and electron localization function shows that， there are two kinds of W—O bonds， of which the W—O1 long bond is ionic bond， and the W—O2 short bond is covalent bond； the metal cations form ionic bonds with O atoms.Each type of tungstate exhibits differences in dielectric functions at different directions. A larger Δε has a positive impact on the birefringence Δn. As the radius of the metal cation with d¹⁰ electronic configuration increases， the birefringence of the crystal decreases. The birefringence of ZnWO₄， CdWO₄ and HgWO₄ are 0.192， 0.187 and 0.078 at 1 064 nm. Among the three systems， ZnWO₄ and CdWO₄ show larger birefringence and anisotropy.