Spent ion exchange resins produced by nuclear power plants are radioactive organic waste. Until now, there is no satisfactory industrial treatment. Supercritical water gasification (SCWG) of cationic ion exchange resin (CIER) used in nuclear power plants was carried out in a batch reactor in this study. Results showed that the gasification efficiency increased with the growth of temperature (550–750 °C), addition of alkali homogeneous catalyst (K₂CO₃), proper ratio loading of catalyst to CIER (1:1), decrease of feed concentration (2–10 wt%) and extension of residence time (10–60 min). Carbon gasification efficiency was up to 97.98% with K₂CO₃ added and 30 min at 750 °C in the batch reactor. The gaseous products mainly consist of H₂, CO, CO₂ and CH₄. The GC–MS analysis showed that the organic component in liquid products was mainly composed of benzene, monocycle arenes, phenol group and polycyclic aromatic hydrocarbons. Based on the experimental results, the formation and gasification pathways of CIER in SCW were proposed.