<p>Flexible photovoltaic (PV) support systems have low stiffness, low damping, and may suffer from aerodynamic instability, especially fluttering, under wind loads. Reliable structural modal parameters are essential for studying aerodynamic instability. While some study investigated the low-order modal parameters of flexible PV supports, high-order modal parameters from field-measurement remain scare. This study conducts a comprehensive field modal testing on flexible PV support structure, integrating motion adaptive vision-based measurement and velocity sensor measurement. Subsequent modal identification method combines the variational mode decomposition (VMD), smoothed energy separation algorithm, half-cycle energy operator, and VMD-based mode shape identification method. Based on the proposed field modal testing and modal parameter identification method, the high-order modal parameters of flexible PV support structure are identified in the first time. The identified frequencies are further utilized to update the finite element (FE) model through particle swarm optimization with the cable tension reduction, column modeling, and the metal frames of the PV panels as the update parameters. The FE model updating significantly reduced the discrepancy in modal frequencies between the FE and the field-measurements. Moreover, the mode shapes from the updated FE model and the field measurements are highly consistent. Therefore, such field modal testing and mode identification method can accurately identify the high-order modal frequencies, damping ratios and spatial mode shapes of the flexible PV support structure.</p>