A modal test method based on videogrammetric for large flexible structure on orbit is presented. The methods of 3D dynamic reconstruction, camera calibration and pixel extraction are described. A ground experiment is performed using a kind of antenna model and two fast cameras. Image data is acquired frame by frame during the free vibration period of the model, and vibration signals are obtained by a time series of images. The ERA method is applied to identify the modal parameters of the antenna model, and the experimental results show that the videogrammetric is a promising method for on-orbit vibration measurement which avoids the difficulty of installing accelerometers on the flexible structures.