Abstract: The threedimensional quasisteady flow fields of PE-HD in three kinds of kneading blocks were calculated by using Polyflow software. The model for dispersive mixing of carbon black in polymer melts was introduced. The size distribution of carbon black agglomerated in different kneading blocks was calculated. The dispersive mixing effect of carbon black in PE-HD in the three kinds of kneading blocks was compared. The numerical results showed that the shearing and stretching was stronger and dispersive mixing effect was better for the kneading block with wider kneading discs.