A series-type photovoltaic high-voltage direct current (DC) grid-connected converter topological circuit and a modulation method thereof, wherein the topological circuit includes a high-frequency transformer configured to isolate a primary side circuit from a secondary side circuit. The primary side circuit includes a high-frequency full-bridge inverter circuit, an active-clamping circuit, an input capacitor C1, an input diode D0, and a boost inductor L1 and adjusts the boost mode and buck mode of the topological circuit. The secondary side circuit includes a high-frequency rectifying circuit, a filter capacitor C3 and a filter capacitor C4, and rectifies and filters an output voltage of the high-frequency transformer. The secondary side circuit further includes a switch tube Q5, and the switch tube Q5 adjusts the secondary side circuit into a voltage multiplication circuit to double the output voltage of the high-frequency transformer.