To enhance the robust stability of the dc-link voltage in the photovoltaic (PV) grid-connected system, a modified linear active disturbance rejection control (LADRC)-based regulation strategy is presented in this paper. The proposed control strategy is equipped with the cascaded extended state observer, which can supplement the disturbance information not estimated by the conventional one, thereby achieving a relatively fast and accurate disturbance reconstruction. The tracking performance and disturbance rejection performance of the modified LADRC are discussed and studied in the frequency domain. Finally, the experimental results are provided to verify the theoretical analysis.