Reef paleo-oil reservoirs in the Nanpanjiang Basin were mainly distributed in Permian and Devonian strata. Reservoir of paleo-oil is mainly bioherm limestone. Bitumen mainly occurs in cavities and fractures, and also in matrix pores and biological coelomata. The maturity of the bitumen is very high, and the atomic ratio of hydrogen to carbon of the bitumen is less than 0. 4. So, the bitumen is mainly composed of carbon residue, which is the reason that there is no extract in the bitumen by non-polarity or polarity extracting. Based on the geochemistry of paleo-oil reservoir, it is concluded that the bitumen in paleo-oil reservoir is mainly from Devonian source rock and secondly from Permian source rock in the Nanpanjiang Basin. The bitumen of the paleo-oil reservoirs in the Nanpanjiang Basin is pyrobitumen formed of oil cracking under high temperature and pressure in depth, much different from biodegradation bitumen and asphaltene bitumen.