Abstract: To investigate the influence of temperature and heat conduction on the diffusion characteristics of self-expanding polymers within planar fractures, the principles of grout chemical reactions were considered. The mass conservation equation of grout components, flow control equation, and fracture heat conduction equation were discretized separately using quasi-three-dimensional and three-dimensional collocated grid finite volume methods. Subsequently, a grout-fracture wall thermal flow-coupled simulation model was established. Iterative control was implemented utilizing the PISO algorithm, enabling the solution of the multi-field coupled system governing the diffusion process of polymer grout injection into fractures. The comparative analysis with results obtained from commercial software demonstrates a good agreement in terms of grout reaction progress, of diffusion characteristics, of system temperature evolution, and of flow field density and pressure distribution between the two methods. Moreover, the simulation results exhibit a favorable consistency with experimental results of polymer grout injection into fractures, validating the applicability and correctness of the established model. This model transforms a three-dimensional problem of fracture injection into a two-dimensional problem, compared with the three-dimensional finite volume method, which significantly reduces the number of fluid elements, decreases modeling complexity, and saves computational time. Thus, it provides a rapid and efficient approach for investigating the impact of thermal-fluid coupling effects on the diffusion behavior of polymer grout in fractures.