Abstract: Coal pyrolysis in arc plasma jet is very complex.Some factors such as Coal Specific Enthalpy ( CSE ) and coal feed rate were discussed.Experiment results showed that coal conversion increased with CSE .With the increase in concentration of coal fed into plasma jet, the volume fraction of acetylene in product gas increased evidently, which led to the improvement of acetylene yield and specific energy requirement of the process.The increase of coal feed rate was not in favor of coal conversion and acetylene yield.Coal feed rate had obvious influence on component distribution, that is the carbon number of hydrocarbon in product gas was less than two with lower feed rate.With the increase of coal feed rate,component distribution became complex and the hydrocarbons with more than three carbons were present in product gas.A reaction mechanism is presented,which suggests that thermal pyrolysis of coal in plasma jet is the first step.The secondary pyrolysis of volatile matter has much more rapid reaction rate than coal pyrolysis,and the volatile matter is assumed to be the precursor of acetylene.Acetylene decomposition is a reversible but not an equilibrium reaction.The kinetic deductions showed that this hypothesis could explain the experimental results very well.