The co-cracking experiment of waste plastics and heavy oil was done in the condition of 400 °C and pressure not higher than 2.0 MPa. The experimental results showed that the yield of heavy oil and coke decreased but the light oil and gas yield increased with the increasing amount of waste plastics. The products of heavy oil’s solidifying point, flash point, viscosity and density decreased and had a good pour point depression effect. Heavy oil containing heat conduction oil and solvent contributed to heat transfer, melting and transport and had the effect of dissolution and co-cracking. It would have a good prospect when the co-cracking of waste plastics and heavy oil was applied to the combination processes of visbreaking and delayed coking and catalytic cracking and delayed coking.