K2CO3-catalyzed steam gasification of petroleum coke at 650-850 degrees C was performed using a laboratory fixed-bed reaction system with an on-line quadruple mass spectrometer. Due to the catalytic effect of K, the catalytic gasification rate exhibited a maximum in the high carbon conversion range, which was different from that in the case of non-catalytic gasification. When the random pore model was used to simulate the catalytic gasification process of petroleum coke, great deviations were found at high carbon conversions. A semi-empirical model (extended random pore model) was proposed on the base of the random pore model. It was found that the extended random pore model could describe well the catalytic gasification profile in the whole carbon conversion range, and the two empirical parameters (alpha and beta) introduced in the extended random pore model could be well correlated with the gasification temperature.