Provided is a method of preparing a pure M1 phase MoVTeNb-oxide catalyst with a high specific surface area, including S1) mixing and dissolving a molybdenum-containing compound, a vanadium-containing compound, a tellurium-containing compound, a niobium-containing compound and a protective agent to obtain a precursor-protective agent mixed solution, in which the protective agent is a surfactant or a small molecule organic acid and a salt thereof; S2) subjecting the precursor-protective agent mixed solution to a hydrothermal reaction to separate out a solid; S3) calcining the solid in an air atmosphere, followed by calcining the same in an inert gas, and then performing a hydrogen peroxide purification treatment to obtain a pure M1 phase MoVTeNb-oxide catalyst. This catalyst exhibits an excellent conversion rate, selectivity, space time yield and stability in the oxidative dehydrogenation reaction of ethane for preparing ethylene.