Abstract: Based on an analysis of the chemical composition and characteristics of oily sludge produced from Ordos basin oilfield and the gasification ash & ash water after mixing with coal water slurry, the chlorine migration in the gasification process of oily sludge-coal water slurry was studied. The results showed that the oily sludge mix ratio is 5% (wt) in the whole slurry, and the ash water composition is basically identical with common coal water slurry. The chlorine in oil sludge-coal water slurry is mainly migrated into ash water during gasification process, with little into the coarse slag and fine dregs. By gasification reaction the chlorine in oily sludge mainly transfers into hydrochloric acid, and no dioxins are formed in the gaseous phase.