Ultrahigh molecular weight polyethylene (UHMWPE) is an excellent property polymer, but its poor processability due to high melt viscosity limits the more wide-ranging application. To improve the processability of UHMWPE composites filled by calcium carbonate (CaCO3), a novel method is reported to modify CaCO3. PE wax coated on the surface of CaCO3 (PEW@CaCO3) can be prepared by acrylic acid–modified CaCO3 (AA-CaCO3) and PE wax. The crystallization and melting behavior of UHMWPE and its composites filled by CaCO3, AA-CaCO3, and PEW@CaCO3 was compared by differential scanning calorimetry. The processability of UHMWPE composites was characterized by torque rheometer. The effect of CaCO3, AA-CaCO3, and PEW@CaCO3 on the crystallization and processability of UHMWPE was discussed.