In this study, cold bonding granulating method was used to produce the fly-ash lightweight insulation with vermiculite as the core. In addition, wet spraying method was employed to model the steel bar condition after sprayed with insulation. Small-scaled specimens were progressed the fire resisting test to inspect the availability of appling fly-ash lightweight material to the insulation engineering on structures. In addition to fly-ash lightweight material, vermiculite, non-granulated fly-ash lightweight material with the same prescription, and vermiculite with fly-ash of different ration were adopted in this study. There therefore would be four series, there binds of bonding ratio, which were composed of twelve binds of materials in different mixing ratios in total. With the same workability, materials were sprayed on the steel sheet torched with thermocouple, and the CNS 12514 specified standard temperature rising cure of buildings on fire was used as heating condition to pregress fire resisting test to understand the relationship among fire resistance, coating thickness and fire resisting duration. Simultaneously tests on compressive strength, adhensive strength and change in water content were undertaken to learn the mechanics property and water-remaining capability of materials. After every test result was compared, in fire resisting duration, to achieve the performance of 2-hours fire resisting duration, the spraying thickness of granulating fly-ash lightweight insulation should be thicker than that of vermiculite insulation by about 3mm. However, the compressive strength of it was two times greater then that of vermiculite insulation, and adhensive strength of it was improved, too. Thus, it was available to apply fly-ash lightweight materials to the insulation engineering of steel structure.