Abstract: The weight average molecular weight,the hydrodynamic radius and gyration radius,the size distribution and the shape of the particles of flocculation PAC and PAC-V in pure water are studied with laser scattering technique.Accompanied with removal efficacy measurements,the study proves that the molecular weight,the size and shape of flocculation strongly affect the removal efficacy,and do not change with the concentration of flocculation,thus provides experimental evidence and theoretical basis for flocculating mechanism.