The invention relates to a preparation method for a semiconductor alloy material MgxZn1-xO, in particular to a method for preparing a semiconductor alloy material MgxZn1-xO with a single cubic phase structure. The method is as follows: firstly, taking the powder mixture of MgO with the molar ratio of 0.32 to 0.61 and ZnO with the molar ratio of 0.68 to 0.39; then, hot-pressure sintering the powder mixture under a pressure of between 4 and 6GPa at a temperature of between1600 and 2000 DEG C to obtain the semiconductor alloy material MgxZn1-xO, which has the single cubic phase structure with the range of the forbidden bandwidth from 3.5 to 5.5eV. The method provides a technical means for manufacturing the semiconductor alloy material MgxZn1-xO (X is more than 0.32 and less than 0.61) in large scale, provides a very suitable new material with high quality for the light electricity device production technical field, and further lays the material foundation for the preparation and realization of ultraviolet detecting devices.