Hydrocarbons in the oil/gas accumulations can seep vertically along the pores, joints, microfractures, fractures, and faults to the surface and form geochemical anomalies, which is the theoretical basis of surface geochemical exploration technique. Most of faults underground have big inclination angle, and are not vertically distributed. It is thought that faults are the dominant pathways for microseepage, the geochemical anomalies formed through faults may deviate from the vertical projection of actual hydrocarbon accumulation on the surface. Such a point of view will arouse doubt among geologists about the role of surface geochemistry exploration technique in predicting hydrocarbon accumulations underground. Based on a theoretical model of fault block hydrocarbon accumulation, the authors developed an experimental apparatus to simulate the phenomena of hydrocarbon microseepage of the fault block hydrocarbon accumulations. The effect of faults on vertical hydrocarbon microseepage was studied. The results of the simulation experiments show that faults are not the only dominant pathways of hydrocarbon microseepage from the fault block hydrocarbon accumulations, the fractures and micro-fractures system developed widely in the strata are also the important factors to decide the distribution of surface geochemical anomalies, and vertical hydrocarbon microseepage exists objectively. Whether faults are the dominant pathways of hydrocarbon microseepage or not depends on the sealing capability of faults. The study also shows that the sampling method which is most suitable for delineating the oil and gas target is the highest density grid.