VO2 attracts much attention due to its metal-insulator transition. Alloying VO2 with MgO and GeO2 allows the band gap and the transition temperature to be varied. We find that the spin order plays a key role in creating the band gap in the low-temperature M1 phase. For MgO alloying, the alloying fraction n(MgnV1−nO2−n) is varied from 12.5 to 33.3%. The minimum band gap does not change without a structural rearrangement because both band edges of insulating VO2 consist of only V 3d states on sixfold-coordinated V sites. A crystal search finds that if the Mg fraction in the alloy is large enough (>20%), fivefold-coordinated V sites can have lower energy than the sixfold sites, and the band gaps are doubled. For GeO2 alloying, the insulating M1 structure reverts to rutile because GeO2 has a rutile phase. The result matches the experimental observation and is very important in guiding VO2's applications such as smart coating and nonlinear resistor.