Abstract: Gas chimney is one of seismic anomalies resulting from vertical gas or fluid migration. It is formed by the combined action of overpressure, low stress and mud shale sealed reservoir. During the formation of gas chimney, large scale methane-rich fluid migrates into gas hydrate stability zone along with it. After it is formed, gas chimney is still a special migration pathway to the later action of fluid and petroleum. Gas chimney is the main pathway for gas migration in Qiongdongnan basin after middle Miocene. Many gas chimneys were found in the distribution zone of bottom simulating reflector (BSR) identified from seismic data. The characteristics of gas chimney are biogenetic mud diapirs by analyzing the parameters of interval velocity, fluid potential,mud content and well data.