Abstract: In order to improve the st rength of the quartz fiber/ SiO₂ composite , and escape the reduction of themechanical property by crystallization of the quartz fiber , the crystallization is studied in detail. The chemical bondst ructure of the quartz fiber was examined by FT-IR , and the crystallization process of the quartz fiber was analyzedby DSC and XRD. The crystallization photograph and production were observed by SEM and TEM. The resultsindicate that there are some Si —OH bonds in the quartz fiber and the crystallization process is cont rolled by st ructure rearrangement which can be seen in the DSC curve. The crystallization start s at 950 ℃ and get s to the top at1400 ℃. The XRD result shows that the product is onlyα-cristobalite , and the beginning temperature is lower thanthat of the bulk quartz glass. The Si —OH bond , impurity and phase interface are the important factors for the crystallization temperature of the quartz fiber to be lower than that of the quartz glass.