Due to the increasingly tight energy supply situation, thermal insulation mortar is more and more widely used in the exterior wall insulation layer of buildings in various countries. However, the existing academic papers have less research on the key properties of thermal insulation mortar such as fire resistance and economic feasibility. Based on the previous research results, this study selected silica fume as an admixture to improve the comprehensive performance of insulation mortar. The goal is to develop a high-performance fireproof insulation mortar. This paper focuses on the fire resistance of the improved insulation mortar. The results show that silica fume mixed into the mortar will play a fine particle filling and hydration gelation cooperation, and the amount of silica fume mixed from 0 to 10% can significantly improve the bond strength and compressive strength of the mortar. For the thermal conductivity and dry density of mortar, there is a certain increase in the range of silica fume dosing from 0 to 4%, while the range of silica fume dosing from 4% to 10% decreases again. Silica fume has a favorable effect on improving the fire resistance of insulating mortar, and the mortar with 10% admixture of silica fume has about 28.30% lower mass loss rate after high temperature and about 14.73% higher relative compressive strength after high temperature after 28 days of maintenance. The final selected optimum admixture of silica fume is 10%, and the best ratio of raw materials is cement: aggregate: water: dispersible emulsion powder: fly ash: diabase rock powder: AOS foaming agent: gelatin: silica fume = 1: 1.67: 2: 0.045: 0.15: 0.225: 0.035: 0.02: 0.138.