In order to obtain the molecular structure，the of polycarbosilanes relationship between molecular hydrodynamics and molecular mass and the concentration dependence of reduced viscosity have been investigated.The results indicated that for PCS，absolute weight-average molecular mass M_w=1.098×10⁴ g/mol，molecular weight distribution MWD=6.7，the second virial coefficient A₂=1.57×10^-3 cm³·mol/g²，Huggins constant k’=1.85，the scaling exponent b between hydrodynamic radius and molecular mass=0.21.At normal atmospheric temperature，tetrahydrofuran（THF） is a thermodynamically good solvent for PCS.And PCS macromolecules are characterized by compact structure which is not in according with the characteristics of linear polymers.