Abstract: By studies of more than 100 structures of Tc compounds reported up to date, it is found that compared with other factors, the oxidation state(OS) of Tc has little effect on the bond length. From the facts that, the Tc remains stable at a certain relatively higher OS, despite the coexistence of the reductant in a largely excessive amount and the existence of a number of fractional OS compounds, it is concluded that the coordination environment is the essential factor governing what an OS will be achieved, and deserves more attention in the synthesis of a Tc compound of a desired OS.