Ocean internal wave is an important mesoscale ocean phenomenon. Spaceborne synthetic aperture radar （SAR） is one of the commonly used observation methods. Tiangong-2 interferometric imaging altimeter （TG2-InIRA） launched in 2016 is a new microwave sensor for ocean observation， which observes the sea surface at small incidence angles of 1°~8°， and the internal wave imaging model applicable to such range of incidence angles has not been reported before. An internal wave imaging model is established based on TG2-InIRA images， and the imaging characteristics of ocean internal waves at small incident angles are analyzed by one-dimensional simulation. The internal wave parameters were retrieved by Variational Mode Decomposition （VMD）， and the SAR image for the same internal wave obtained by Sentinel-1 4 hours and 13 minutes later was used for comparison and validation. The results show that the light and dark sequence of the observed internal wave by TG2-InIRA is opposite to that by Sentinel-1 SAR， and the relative differences between the retrieved widths and amplitudes from TG2-InIRA and Sentinel-1 SAR images are about 8.14% and 15.62%， respectively， and their variations are accorded with the variation law for the internal wave propagation， and thus， the detection ability of internal wave is demonstrated. The statistical analysis results from 40 and 19 internal wave images obtained by TG2-InIRA and Sentinel-1 SAR in the South China Sea region respectively show that over 80% of the actual images have the opposite light and dark stripes， which is consistent with the established model and simulation conclusions.