Abstract: Two thermotropic copolyeters BP-LCP and BPM-LCP have been synthesised.A series of in-situ somposites which composed of polysulfone and copolyesters with different molecular weight have been prepared.The effects of chain structure,molecular weight and content of.LCP on formation of microfiber have been discussed,and the action of shear and stretch on microfiber been investigated.It is proposed that the lower of the compatibility, the better of the microfiber.And the results obtained show that the remakable microfiber is formed when the content of high molecular weight BP-LCP is more.