In recent years, the natural gas discovery has proved that the Oligocene lobe complex in the Rovuma Basin, located at the edge of the passive continent of East Africa, has great potential for resources and a good prospect for exploration. The lobe complex is characterized by coarse grain, huge thickness, a low ratio of width to thickness and unilateral migration, which is obviously different from conventional sheet sand. The lithology characteristics, electrical response and seismic reflection characteristics of a deep- water sedimentary lobe complex were analyzed by using the core, logging and seismic information obtained during oil and gas exploration. The internal composition of the different hierarchies of the lobe complex was identified by means of seismic profile and coherence slices along horizon, and the deposition process of the lobe complex was analyzed. Meanwhile, the main factors affecting the deposition of the lobe complex were also discussed. The study shows that the Oligocene lobe complex in the Rovuma Basin has “rootless” external morphology and complex internal reflection configuration. It can be divided into four hierarchies: the lobe complex, the lobe, the lobe element, layer and the layer group. The lobe complex formed after the mass transport deposition and before the channel complex deposition was the product of the late falling- stage systems tract. It is inferred that the sea level fluctuate rate affects the vertical distribution of the lobe complex reservoir. The greater the base level descending rate, the greater the thickness of monolayer sandstone. There is a positive correlation between the two. The deposition of the lobe complex has undergone multiple stages of lobe deposition. In the early stage, the restricted deposition in the way of backfilling, the non restrictive deposition of mid- term multiphase lateral migration, and the mud- rich channels with high bending and migration at the end of the boundary were last phase. From the feeder channel to the distal end of the lobe complex, the ability to carry coarse particles gradually decreases with reduction gravity flow intensity. The sedimentary thickness of the near and proximate part is large, the ratio of sand to mud is high, the sedimentary thickness of the edge and the distal side is thinner, and the ratio of sand to mud decreases. The sand to mud ratio of the proximate body is 2~3 times that of the feeder mouth and the far side. The shape of the continental shelf, the relationship between the gradient of the slope and the sea level affect the location, the external form and the way of migration of the lobe complex. The narrow continental shelf and steep continental slope promote the near source accumulation of coarse sand- rich lobe complexes. When the terrain gradient is consistent with the base level, the turbidity currents in the slope do not deposit, leading to the formation of the “rootless” of the lobe complex. The slope changes along the slope strike to cause lateral migration of the lobe.