The research to the formation mechanisms of modern karst subterranean streams can be a "key" to reveal the genesis of space distribution of reservoirs full of large paleokarstic fractures and caves, which is useful to guide oil and gas exploration. There is an underground river at Zhaidi in Guilin, Guangxi province. Based on studies of field geological survey, tracer tests, geophysical and drilling data, it has been clear how the large karstic fracture-cave space distributes within the underground network of Zhaidi River with total 10.6km length of subterranean stream pipelines. It is proved that geomorphology, stream network, lithology and faults are the factors affecting development of the underground river network. In light of the research of Zhaidi Underground River, the case is applied to analysis of a paleokarst underground river that distributes within Ordovician karst fractured-caved reservoirs in Halahatang Field, Northern Tarim Basin. The network of the paleokarst underground river and the space distribution of large karstic fracture-cave system in it are depicted according to the comprehensive analysis of karst geological background, the palaeogeomorphology, ancient water system, and ancient hydrodynamic conditions, combined with 3-D seismic technology. Exploration result has indicated the fact that economical productions are obtained in all of wells drilled in the underground river pipelines.