Based on true sandstone micro-model, an experiment of gas-drive-water was performed to simulate the secondary migration in the sandstone porous media. The migration course and characteristics of gas in pores and throats are observed. Furthermore, the micro-mechanisms of gas migration are analyzed and discussed. It is found that the migration pathways are usually flexuous and look like branches of tree. Gas always migrates forward along the limited pathway where the capillary force is lowest. The migration speed is inhomogeneous because of the inhomogeneous porous structure and the change of migration drive. The snap-off is prevalent in water-wet media whose ratio of pore and throats is large. The snap-off is disadvantageous for gas migration because it will increase the migration resistance. It is also observed that a sudden shake can promote gas migration.