Accurate image navigation validation (INV) is essential for the longwave (LW) bands of the geostationary interferometric infrared sounder (GIIRS) onboard the Fengyun 4A (FY-4A) satellite. However, few scientific peer-reviewed papers have been reported to date. In this study, we present, for the first time worldwide, a satellite-ground integrated INV technique applied to the FY-4A GIIRS’s LW, leveraging the ground-based laser positioning system (GLPS) to assess its navigation precision. The GLPS is designed to precisely and automatically point at the satellite and transmits laser signals whose center wavelength is predesigned and thus can be detected by GIIRS’s LW detectors. Two observation modes are designed for GIIRS when the laser operations are scheduled, namely, dwell observation mode and step scanning mode. For the data analysis, three methods are proposed for different stages of data processing. A simple but universal and efficient algorithm called laser index is proposed for laser signal detection. Two customized algorithms are used for the designed laser operations to obtain the image navigation deviations in dwell observation and step scanning modes. The laser tests demonstrate that east-to-west navigation deviations are within 0.35 pixels, and north-to-south navigation deviations are within 0.45 pixels, which is consistent with the results of equivalent results from the visible band. The result analysis of the laser data demonstrates that the proposed methods are effective and precise, and it is a reliable tool to verify the image navigation results through GLPS.