The invention discloses an ultralow-density cement slurry suspension stabilizer applicable to low-temperature-to-high-temperature conditions. The suspension stabilizer is prepared from the following ingredients in percentage by mass: 45% to 60% of subnanometer silica, 40% to 55% of micron amorphous silica and 5% to 8% of micron asphalt powder. The subnanometer silica contains the silicon dioxide content of 95% or more by mass, is white or greyish-white solid powder and has the median particle size lower than 200nm-450nm; the micron amorphous silica contains the amorphous silicon dioxide content of 85% or more by mass, is white or greyish-white solid powder and has the median particle size lower than 10mm-30mm; and the micron asphalt powder contains the asphalt content of 85% or more by mass, has a softening point of 30 DEG C to 130 DEG C and has the median particle size lower than 20mm-50mm. The suspension stabilizer can cause low thickening at normal temperature to facilitate the blending of ultralow-density cement slurry and can still have good suspending characteristics at high temperature to prevent the ultralow-density cement slurry from being settled and layered, the design performance of the cement slurry is kept, and the demands of oilfields on low-temperature-to-high-temperature ultralow-pressure stratum well cementation are met, so that the suspension stabilizer has abroad application prospect.