The effects of alkalis on the dechlorination of chlorinated organic substances were systematically studied with molecular dynamics (MD) simulation and experiment method. The association interaction of alkali appears in the SCW solution, which affects the dechlorination reaction performance. The ion association interactions of sodium hydroxide and potassium hydroxide in the supercritical water (SCW) were investigated by analyzing Radical Distribution Function in a temperature range of 623.15-823.15 K and density range of 0.1-0.4 g/cm(3). The simulation results indicated that Na+, K+ and OH- associated directly, which is bad for the dechlorination of o-chlorophenol. Meanwhile, the ion association interaction decreased with density, but increased with temperature. The effects of sodium hydroxide and potassium hydroxide on the dechlorination of o-chlorophenol were compared. The results showed that the addition of alkalis accelerated the dechlorination of o-chlorophenol, and the effect of potassium hydroxide was better than that of sodium hydroxide. The simulation results were proved by experiment. (C) 2014 Elsevier B.V. All rights reserved.