Helical spin texture with the remarkably high spin polarizations of topological surface states have been firstly uncovered by the innovative spin- and angle-resolved photoemission spectroscopy for two promising topological insulator Bi₂Te₂Se and Bi₂Se₂Te. Their highly spin-polarized natures are found to be persistent across the Dirac point in both compounds. This novel finding paves a pathway to extending the utilization of topological surface state of these compounds for future spintronic applications.