The invention provides a photovoltaic grid-connected power generation system based on middle and high voltage direct current access. The system comprises at least one middle and high voltage direct current power generation unit and a middle and high voltage centralized PV grid-connected inverter. Each of the direct current power generation unit comprises multiple groups of PV arrays and cascaded direct current boost units. Each group of the PV arrays comprises a plurality of arrays which are connected in parallel. The output end of each group of PV arrays is connected to the input end of one cascaded direct current boost unit. The output end of the cascaded direct current boost unit is connected to one path of middle voltage and high voltage direct current bus and is used for raising the direct current voltage outputted by each group of PV arrays and carrying out bus out in a mode of series connection to the path of middle voltage and high voltage direct current bus. Each path of middle voltage and high voltage direct current bus which is respectively connected to the output end of each of the cascaded direct current boost units is connected in parallel to form a path of middle voltage and high voltage direct current bus which then is connected to the direct current side of the middle and high voltage centralized PV grid-connected inverter, and the alternating current side is connected to a middle and high voltage alternating current power grid. According to the photovoltaic grid-connected power generation system, the line loss can be reduced, and the cost can be reduced.