The oxygen content of the SiAlCO fibers was a key for the transformation from SiAlCO fibers to dense stoichiometric Si C fibers after sintering at 1700 ℃,which was mainly introduced during curing process.The novel preoxidation-thermal curing method was applied to the conversion of polyaluminocarbosilane(PACS) fibers and the oxygen content of the SiAlCO fibers as-pyrolyzed was adjustable in 10% —13%(mass fraction).A minimal degree of preoxidation of the PACS green fibers,which performed at 190 ℃ for 4h leading to 7.87%(mass fraction) oxygen pick-up,is necessary for their further thermal-curing.Then,the preoxidation fibers formed crosslinking structure after thermal-curing at 450 ℃ under N2 flow.The curing process was investigated by gel permeation chromatography(GPC),infrared spectrum(IR) and thermogravimetric analysis-mass spectra(TG-MS).The results show that the Si—OH bonds are formed after the Si—H bonds in the structure of PACS fibers reacting with oxygen molecular during preoxidation.Additionally,partial Si—OH bonds could react with each other continuously to form Si—O—Si structure,resulting in molecular increase.During the thermal-curing process,the residue of Si—OH further react with each other at lower than300 ℃.The formation of Si—CH2—Si structure resulted from the reaction between Si—H bond and Si—CH3 bond happened in the range of 300—450 ℃.