Polycarbosilane（PCS）was synthesized from the distilled fractions of liquid polysilane (LPS). By adopting the GPC technique，the influence of different distilled fractions of LPS on the molecular weight and their distribution of PCS was discussed in detail. It was found that the total average yield of PCS synthesized from the distilled fractions of LPS is about 35wt% higher than that of PCS synthesized from the untreated LPS under the same condition. In addition, PCS with a super high molecule weight can be synthesized from the distilled fractions of LPS treated below 200℃.