The invention relate to alkyloxy vanadium compounds and a preparing method thereof. The method includes putting a reactor into a low-temperature cold trap, maintaining the temperature in a range from -40 DEG C to 10 DEG C, adding a vanadium compound into the reactor, slowly adding an alcohol compound, bubbling in high-purity nitrogen, and continuously feeding the high-purity nitrogen after the addition of the alcohol compound is finished until noncondensable gas produced in a reaction is fully blew out, thus preparing an alkyloxy vanadium compound. Clean alkyloxy vanadium compound products can be prepared through the method. Ethylene-alpha-olefin-conjugated diene random copolymers narrow in distribution can be synthesized through adopting the alkyloxy vanadium compounds as main catalysts and adopting alkyl aluminium halide as a cocatalyst.