In the preparation of SiC ceramic fibers based on precursor polycarbosilane, the crosslinking treatment is a neccessary process to maintain the fiber morphology and improve the ceramic yield. In this study, polycarbosilane containing acrylate group (A-PCS) was used as raw material, and the thermal free radical initiator was introduced to realize the crosslinking formation during the pyrolysis process. FT-IR and DSC were used to analyze the influence of initiator content on crosslinking degree, crosslinking rate and thermal degradation rate of A-PCS; TG, elemental analysis and XRD were used to analyze the evolution of ceramic yield, composition and amorphous change with temperature. The introduction of free radical thermal initiator can improve the crosslinking rate of acrylate group in A-PCS and reduce the thermal weight loss at the crosslinking stage. When free radical thermal initiator (weight percent 1%) was added, the acrylate group was consumed completely after heating to 250 ℃ at 5 ℃/min and the ceramic yield at 1500 ℃ was 69.5%. A-PCS fibers with diameter of 2-5 μm were obtained by electrospinning process, and then transformed into SiC fibers by subsequent pyrolysis. The morphology of the SiC fibers was regular with no fusion phenomenon. In addition, with the increase of pyrolysis temperature, the amorphous SiC fiber can be transformed into crystalline structure.