Preparation of nonderived water-soluble chitosan with high molecular weight is of great significance to the innovation of materials and its application.In this paper,the forced penetration method for preparing a natural water-soluble chitosan have been investigated.Under the action of vacuum,the concentrated alkali was forced to infiltrate into the micropore of chitin particles.This has accelerated the swelling of chitin,as well as the mass transfer process of NaOH,and thus form an approximate homogeneous environment of deacetylation.By controlling the degree of deacetylation of about 50%,a water-soluble chitosan(WSC) can be obtained.The apparent viscosity,FT-IR,X-ray diffraction(XRD) and differential scanning calorimetry(DSC) were applied to estimate the structure and properties of WSC.The results showed that water-soluble chitosan and the traditional chitosan have no essential difference.The difference is that the WSC prepared with forced penetration method has more amorphous structure,weakened intermolecular hydrogen bonds and good water solubility.