The invention provides a self-adaptive dynamic reactive power compensation method for photovoltaic grid-connection inverter. The method comprises the following steps: 1) acquiring direct current voltage command value (marked in the figure) and the current command value (marked in the figure) under voltage-current double-loop control; 2) disconnecting the DC-voltage outer-loop control of the double ring control; 3) establishing a new outer ring control for the power grid voltage including an outer ring control circuit based on a self-adaptive controller and an inner control circuit based on a PIR controller; 4) disconnecting the outer ring control circuit based on the self-adaptive controller when the power grid voltage is recovered to normal within a preset time; and 5) assigning the direct current voltage command value (marked in the figure) to the reference voltage of an MPPT controller in the direct current voltage outer ring control; and conducting another time the outer ring control of the direct current voltage of the power grid and the inner ring control of the grid-connection current. Compared with the prior art, the self-adaptive dynamic reactive power compensation method for photovoltaic grid-connection inverter of the invention is capable of switching between different strategies quickly when the voltage of a power grid is detected to have dropped so as to ensure photovoltaic grid-connection.