Abstract: HJQ(Hangjinqi) area is located in the Yishan slope and HJQ step-fault zone in northern Ordos. In spite of some previous researches for targeting favorable prospects, the exploration success rate is approximately 25% because of a complicated gas-bearing mechanism in this area. The main problem lies in how to improve the exploration success rate and to make clear the mechanism of hydrocarbon accumulation. Through analyzing the reflections, distributions and characteristics of logging curves for source rocks and reservoirs in both industrial gas wells and dry wells, we have found out their distinctions of reflectance and given a summary of three reflectance signatures. By using seismic cross hole reflection technique, it shows that the target has a strong reflection, consistent phase continuance and proper events display in the down dip direction within the tectonic setting; it also proves that where the events are merged or thinned out in the up dip direction it is the most favorable location for oil and gas accumulation. Thus, it concludes that hydrocarbon accumulations depend less on the degree of development of source rocks, but more on the existence of structural traps and lateral variations of reservoirs; that is, structural trapping is prerequisite for hydrocarbon accumulations, while depositional trapping essential. All researches discussed in this paper can be taken as a database and reference for the next round drilling project.