This work reports a study of the co-gasification reactivity of petcoke with lignite by using a thermal gravimetric analyzer. The effect of fixed carbon, volatiles, and minerals in lignite on CO2 gasification of petcoke was studied over a temperature range of 850-1000 degrees C. The co-gasification kinetics of petcoke with lignite were also studied. Results showed that the fixed carbon and volatiles from lignite had a slightly positive impact on petcoke gasification, while the poor reactivity of petcoke was improved significantly by coal char or ash. The co-gasification reactivity was influenced by the mixing ratio. It was found that the minerals played a central role on co-gasification. Active components such as Fe2O3/CaO had a catalytic effect, while inert components such as Al2O3/SiO2 had no or even negative effect. The catalytic effect of simulated ash depended on the amounts of Fe2O3 and CaO. The shrink core model and apparent kinetic model (AKM) were selected to describe the co-gasification process. Results showed that AKM was more suitable for simulation of co-gasification. By co-gasifying, the activation energy was reduced greatly which indicated the existence of a synergistic effect derived from active minerals in lignite.