Abstract: An advanced topology is introduced to improve the converting efficiency of the double-stage PV grid-tied inverter, which includes a by-pass relay between PV cell and bus capacitance. The on-off switch of relay and two working modes of the inverter are determined by the output signal of hysteresis comparator of which input signal is the voltage of PV cell. The first-stage boosted circuit stops working and the by-pass relay picks up which the current of main circuit goes through. The second-stage inverter realizes max power point tracking and grid connection, so the dissipation caused by boost inductance and diode disappears. The topology and strategy are not only realized in Matlab, but also verified in a 3kW single-phase double-stage photovoltaic grid-tied inverter.