The invention discloses a roof greening and overhead photovoltaic cell panel combined heat insulation system, and relates to a roof heat insulation system. At present, both roof greening and erection of a photovoltaic cell panel are carried out independently, and a roof can only be subject to one of the both, thereby causing waste of roof space, insufficient resource utilization and non-ideal heat insulation effect. The roof greening and overhead photovoltaic cell panel combined heat insulation system is characterized by comprising a greening vegetable layer arranged on the roof and a photovoltaic cell panel group erected on the greening vegetable layer, wherein the cell panel group comprises a plurality of cell panels which are distributed at intervals to enable the greening vegetable layer to be irradiated by leak light, and a rain water collecting device is arranged among the cell panels and the greening vegetable layer. By simultaneously arranging the photovoltaic cell panels and the greening vegetable layer on the roof, the invention fully makes use of the roof space, enhances the heat insulation and heat preservation effects and simultaneously combines the advantages of the cell panels and the greening vegetable layer.