The discovery of quantum spin Hall effect engendered a new chapter of topological materials research in condensed matter physics and materials science.Although long sought after,quantum spin Hall effect only has been observed in the engineered 2D quantum well structures such as HgTe/CdTe and InAs/GaSb.And none of the current 2D materials are confirmed to be quantum spin Hall insulator,i.e.exhibiting quantized conductance.In this talk,I will introduce some of our recent theoretical works about the topological phases in 2D and 3D transition metal chalcogenides.Based on first-principles calculations,we predict monolayer MX2 (M=Mo.W;X=S,Se,Te)of 1Tstructure could exhibit quantum spin Hall effect and their topology can be easily tuned by external electric field,which motivated us to propose a new type of transistor,called topological field transistor.More recently,we found another new class of transition metal chalcogenides MMTe4 (M=Nb,Ta;M=Ir,Rh) could be quantum spin Hall insulators in 2D and Weyl semimetals in 3D.