The high chlorine content in municipal solid waste (MSW) was caused by the large use of polyvinyl chloride (PVC). The efficient removal of chlorine, especially organic chlorine, by hydrothermal reaction was the premise to achieve harmless treatment and resource utilization of waste. The plastic components in MSW were complex and organic chlorine mainly came from PVC. Therefore, it was of great significance to study the factors affecting chlorine migration characteristics in PVC hydrothermal dechlorination. Two types of PVC (HB-65 and S-65) and polyethylene (PE), polypropylene (PP), polystyrene (PS), acrylonitrile-butadiene-styrene (ABS) were selected as raw materials to explore the effects of PVC's own performance and hydrothermal conditions on chlorine removal and investigate the characteristics of chlorine migration in the hydrothermal reaction of mixed plastics. The results showed that PVC's own performance was the internal factor affecting the hydrothermal dechlorination. Hydrothermal conditions such as hydrothermal temperature, residence time and reactant concentration were the key external factors affecting the hydrothermal dechlorination. There was a synergistic effect in the mixed plastics hydrothermal reaction due to different thermal expansion. The addition of PP and ABS decreased the dechlorination rate of PVCHB-65 by 71.66% and 70.96%, respectively, and decreased the dechlorination rate of PVCS-65 by 19.05% and 18.15%, respectively. The addition of PE and PS decreased dechlorination rate of PVCHB-65 by 71.06% and 43.06% respectively, while increased the dechlorination rate of PVCS-65 by 8.20% and 46.70%, respectively.