In order to solve the problems of image quality evaluation, imaging link analysis and subsequent processing algorithm verification due to the lack of in-orbit data before satellite launch, an in-orbit geometric imaging simulation method for long-linear-array and whisk-broom (LLAWB) thermal infrared imager (TIRI) based on ray tracing is proposed. Firstly, according to the structure and imaging characteristics of the optical system, the rigorous geometric imaging model of the LLAWB TIRI is constructed. Then, based on the simulation attitude and orbit parameters, auxiliary DOM and DEM data, the spatial projection and imaging simulation of pixel visual vector are realized by ray tracing and re-projection algorithm. Finally, a geometric calibration method based on "generalized" correction matrix is proposed to modify the positioning model and improve the positioning accuracy of simulation images. Experimental results show that the proposed method can be used to simulate the geometric imaging of any orbit position for the LLAWB TIRI, and the positioning accuracy of the simulation image is better than two pixels after calibration. This research provides a new idea for in-orbit geometric imaging simulation of space optical payloads, and is of great significance to the error analysis, geometric positioning and calibration of imaging links.