This study presents an InSAR flight experiment of the latest mission using helicopter dual-band Synthetic Aperture Radar system (HD-SAR), conducted in southern China by the Xi'an Institute of Space Radio Technology. The HD-SAR system is a dual-band polarization radar based on a helicopter platform, designed for rapid installation and high integration. In every frequency band, the dual receiving channel architecture activates the InSAR mode. High-frequency and low-frequency digital elevation models (DEMs) provide differing benefits depending on the scenario because of the various impacts of ground object scattering qualities. Both high-coherence and low-coherence sectors can achieve optimal performance through the use of dual-band fusion technology. This paper presents the system design and key parameters first. The flying experiments and antenna installation plans for InSAR mode on the Sikorsky S-76 helicopter are described in the section that follows. The results showed that in hilly areas, the relative elevation accuracies of the dual-band fusion DEMs improved by 32% and 25% respectively, whereas the relative elevation accuracies of the C-band and Ku-band DEMs were less than 3 meters. SAR and InSAR mode flight experiments have demonstrated that the HD-SAR system is suitable for most high-resolution detection and interferometry mapping scenarios.