The invention provides a BiCuSeO-based thermoelectric material collaboratively optimized by a variable valence element and a preparation method thereof. The chemical formula of the BiCuSeO-based thermoelectric material collaboratively optimized by a variable valence element is Bi1-xMxCuSeO, wherein the M is selected from an element having the valence of +2 or +3, and the x is an atomic percentageof the doped element and is 0-1. The invention further discloses a preparation method of the BiCuSeO-based thermoelectric material collaboratively optimized by a variable valence element, which mainlycomprises solid-phase reaction, high-energy ball milling and hot-press sintering. The thermoelectric material has high electrical conductivity, good Seebeck coefficient and low thermal conductivity.