The earthquake safety of the Chengdu City has been a focus issue since the Wenchuan big earthquake. This paper will talk about the safety of Chengdu urban area in an earthquake based on the basic geological structures and sedimentary features in Chengdu and its neighborhood area. Devastating earthquakes usually occur at active huge fault belts,and are of repetitive. The lithosphere structure of western Sichuan Depression (Chengdu plain) is rigid and stable. Being situated at Chengdu Plain,Chengdu City is on a stable tectonic unit. There is no large fault under the city. There is no record about devastating earthquake in Chengdu Plain in history. Thus,there is no any possibility for a devastating earthquake to occur at Chengdu City. Secondly,Chengdu plain has a thick,good and well-distributed sedimentary cover,which determines that any earthquake occurs in Longmenshan can not make fatal damage to Chengdu urban area.