•The differences on pyrolysis of PVC polymer and plastics were studied for the first time.•More Cl distributed in the pyrolysis char of PVC pipes compared to that of PVC polymer.•Additives in PVC plastics promoted the cracking of heavy fraction in pyrolysis tar. The organic and inorganic additives in PVC plastics cause great difficulties in their actual recycling process, which are different from pure PVC polymer (PVC-PO). In this study, PVC-PO and two commercial PVC plastics were selected and their differences in structure, pyrolysis behavior, chlorine release and migration were compared by FTIR, TG-MS and a fixed-bed pyrolysis reactor. There were more oxygen-containing functional groups and aromatic compounds in the commercial PVC plastics than PVC-PO because of the addition of foaming agents, flame retardants and lubricants. The thermal weight loss of the commercial PVC plastics was divided into three stages due to the decomposition of additives and the releases of CO2 gas, while that of the PVC-PO was two. The pyrolysis tar of two PVC plastics contained 35.72% and 15.71% oxygenated compounds, respectively, while that obtained from PVC-PO contained 96.46% of aromatic compounds. In addition, calcium additives in PVC plastics could promote the cracking of heavy constituents in the volatile, which was favorable for the formation of more light fractions in tar. The pyrolysis gas of PVC-PO was mainly composed of H2 and C1-C4 hydrocarbon gases, while that of PVC plastics contained about 50% of CO2, followed by H2 and hydrocarbon gases. The chlorine content of the PVC-PO (55.88 wt.%) was higher than that of the PVC plastics (13.83 wt.%, 22.77 wt.%). Most of the chlorine in the three PVC samples released as HCl at 220–370 °C, while the peak temperature of dechlorination of the PVC-PO delayed about 8 °C compared to that of PVC plastics and small part of HCl also released at around 475 °C in the pyrolysis of PVC-PO. About 99.90 wt.% of the chlorine was distributed in the gas phase after PVC-PO pyrolysis, while there were 99.85 wt.% and 97.85 wt.% of chlorine was detected in the gas products of two PVC plastics.