In this article, propagation of a methane-air flame and its interaction with coal dust deposits have been investigated. The experiments were conducted in a horizontal flame acceleration tube with a square section. The protodiodes and digital video camera were employed to record the flame propagation. The results indicate that there are three distinguishable stages. In the first stage, gas flame accelerates gradually and deposited dust particles are ingested into air and heated by gas products until ignited at some point. In the second stage, a transient flame of three-front structure can be found, which consists of a leading gas flame, a forward dust flame, and a backward dust flame. In the last stage, the dust flame integrates into the gas flame, which forms a complex gas-dust flame that can continue to propagate. The results also show that the flame is accelerated slightly by the deposited dust but dramatically by obstacles under the present conditions. The terminal flame speed in the tube with the obstacle A of blockage ratio 0.05 or B of blockage ratio 0.10 is about 4 or 16 times as that without obstacles.