The gasification technology of jet-entrained beds has been extensively applied to chemical production and the power generation. Residence time distribution (RTD) is required for modeling, design and optimization of jet-entrained gasifier. RTD in the gasifier was determined experimentally by impulse method. On the basis of the flow pattern, a stochastic model for RTD of materials in the gasifier has been developed, using Markov chain discrete formulation. The predicted results of Markov chain model give a reasonable fit of the experimental data, which shows that the process in the gasifier is stochastic and confirms that there are reflux and short-circuit in the gasifier and the flow pattern is inclined to perfect mixing.