The stability of the intermediate DC-bus voltage of the two-stage photovoltaic inverter is crucial for its good power generating quality and long-term operation. The power generation of photovoltaic inverters is easily affected by environmental factors such as the strength of illumination and temperature, and this power fluctuation can cause significant disturbance on the DC-bus voltage. In order to improve the disturbance resistance of the DC-bus voltage and the control performance of the inverter, a photovoltaic inverter bus voltage control strategy based on improved first-order linear active disturbance rejection control (LADRC) is proposed. The voltage outer loop controller in the dual loop control of the inverter is designed by using improved first-order LADRC. On the basis of the traditional LADRC linear extended state observer, the system control component in the expression of the state variable is removed, so that the observation error equation of the state variable only contains error components related to the system input, which reduces the observation error of the state variable. A new state variable is added and the system control quantity of the previous control cycle is introduced, and total disturbance is re-estimated and compensated based on the total disturbance expression. The control performance of improved LADRC is analyzed in the frequency domain. Compared with the traditional LADRC, the improved LADRC has an increased system bandwidth, enhanced dynamic tracking ability, and smaller disturbance gain in the mid to low frequency range. Simulation and experiments show that the improved LADRC has a shorter regulating time, better system dynamic performance, and the disturbance resistance ability of DC-bus voltage is enhanced.