In recent years, grid-forming control has gradually emerged as an effective approach to enhance the stability of power systems with high renewable energy penetration. However, there exist potential oscillation risks due to inappropriate control parameter settings under different AC grid conditions. To address this issue, a grid-forming PV control strategy based on matching control is proposed, and the small-signal stability mechanism and parameter stability region are studied from a synchronization perspective. First, a transfer function model of the grid-forming PV system is established using the component connection method, and the propagation path of small-signal disturbances is qualitatively analyzed. Then, the dynamic interactions within the system are analyzed based on the synchronization dominant loop to reveal the instability mechanism caused by the mismatch between the control parameters and the equivalent AC grid impedance. On this basis, a small-signal stability index based on the equivalent loop gain is proposed to quantitatively evaluate the impact of various factors on system stability and to determine the stability regions of key control parameters. These results show that a reduction in grid impedance narrows the stability region of the matching control parameters while widening that of the voltage control parameters. Finally, the correctness of the theoretical analysis is verified by time-domain simulations and the control hardware-in-the-loop tests.