With multiple inverters connected to the grid, the power supply system is transformed into a weak grid with low inertia. Grid-forming control of grid-connected inverter is emerging to improve the inverter's transient steady-state performance and anti-interference ability, and grid-forming control also enables the photovoltaic (PV) power generation system to operate in both on-grid mode and off-grid mode, making it as the future direction for new energy grid-connected inverters. In view of the different control objectives and stable operation adjustment of two-stage photovoltaic inverters in on-grid mode and off-grid mode, this paper proposes a coordinated control strategy for the two-stage converters in the PV power generation system with grid-forming inverters in order to achieve stable operation in on-grid mode and off-grid mode. Finally, the corresponding simulation system is built, and the simulation result shows that the PV power generation system can realize MPPT power generation in on-grid mode and provide stable power supply to local load in off-grid mode.