The drying shrinkage, compressive strength, fracture strength, dry density and thermal conductivity of vitrified microsphere insulation mortar were systematically studied when the water to binder ratio are 1.2, 1.3, 1.4 and 1.5. This study reveals the reason that the performance index of vitrified microsphere insulation mortar depends on the different water to binder ratio by mercury test and SEM scanning electron microscope analysis. The results indicate that the drying shrinkage of the vitrified microsphere insulation mortar increases obviously with the increase of water to binder ratio. When the water to binder ratio is fixed, the growth rate of drying shrinkage of vitrified microsphere insulation mortar is rapid in the early stage but becomes slow in the later stage. When the water to binder ratios are 1.3, 1.4, and 1.5, the compressive strength, flexural strength, dry density and thermal conductivity change obviously compared with those of the vitrified microsphere insulation mortar with the water to binder ratio of 1.2. The compressive strength correspondingly decreases by 13.1%, 40.0% and 73.8%, respectively; flexural strength decreases by 18.8%, 35.7%, and 77.7%, respectively; dry density decreases by 8.3%, 19.4%, and 33.3% respectively; and thermal conductivity also decreases by 4.6%, 11.3% and 21.4%, respectively. The structural performance of the vitrified microsphere insulation mortar varies obviously with the change of water to binder ratio. It is also found that the porosity of vitrified microsphere insulation mortar increases with the increase of water to binder ratio by mercury test and SEM analysis.