A fused quartz tube reactor (FQTR) and Raman spectroscopy were employed to investigate the decomposition of H2O2 and o-dichlorobenzene (o-DCB) in hot compressed water (HCW). The results showed that o-DCB can be effectively degraded in HCW, and exhibited applicability as a powerful tool to quantitatively and qualitatively analyze O-2 and CO2 using Raman spectroscopy combined with an FQTR. The decomposition rate of H2O2 reached 95.4% at 8 min, and it completely decomposed after 23 min at 400 degrees C in the closed heating system. When the oxygen stoichiometric ratio (OSR) increased from 50% to 200% after 90 min at 400 degrees C, the degradation rate of o-DCB significantly increased from 67.5% to 100%. The conversion data for the kinetic analysis of o-DCB indicated that the reaction followed pseudo first-order kinetics and exhibited reaction rate constants of k(0.5) = 0.00782 s(-1), k(1.0) = 0.01412 s(-1), k(1.5) = 0.02675 s(-1), and k(2.0) = 0.03509 s(-1), respectively.