Catalytic gasification is a widely accepted approach to utilize petroleum coke for its high-quality products and less pollution. However, catalytic gasification of petroleum coke in fluidized beds is seldom investigated, which has advantages of sufficient heat and mass transfer and high uniformity of temperature. In this study, a microfluidized bed (MFB) was used to study the catalytic gasification behaviors of petroleum coke. Unexpectedly, the potassium carbonate showed poor catalytic effect in the MFB, compared with the results from a thermogravimetric analyzer (TGA). The BET results indicated that the pore structure of petroleum coke was highly undeveloped, leading to the easy separation of catalyst from the surface of coke in the MFB. To improve this situation, we proposed a preheating treatment method to enhance the loading of potassium on coke. The experiment results showed that the preheated petroleum coke had a significantly higher rate of gasification than the impregnated coke, owing to the formation of stable active intermediates. Furthermore, the effects of pretreament conditions were investigated. The FTIR results showed that the ratio of aliphatic hydrocarbons to aromatic hydrocarbons decreased with the increase of preheating temperature and time, while the ratio of oxygen-containing functional groups to aromatic hydrocarbons showed an opposite trend.