Beishan area lies between Tarim platform and North China platform.Due to the complexity of its geological structure,the properties of its basement and its geotectonic characteristics have long been problems of controversy.Based mainly on features of its gravity and magnetic field,this paper deals mainly with its basement properties,its geological structure and,in combination with surface geological investigation data,probes into geological evo lution process,thus providing basic evidence for the discussion of relationship between Tarim platform and North China platform.