Abstract: Existing experiments have observed a novel size effect phenomenon that as the freeze-thaw (FT) cycles increase, size effect of quasi-brittle materials nominal strength changes from the descending size effect to the ascending-descending size effect, and then to the ascending size effect. A physically based model is developed to describe this novel size effect phenomenon and to provide a theoretical basis for the safety service assessment of engineering structures in cold regions. The FT damage of specimen is simplified as the undamaged interior region wrapped by the damaged surface layer based on the fact that the FT damage gradually increases from the center of the specimen to the surface layer. And then, the increasing power function and the exponential decay model are adopted to describe the FT-dependent thickness and the FT-dependent the strength of the damaged surface layer. Based on this, the structural strength model of FT damage is established and validated for quasi-brittle materials. Following this, energy balance size effect model considering the FT cycles for quasi-brittle materials (EBM-FTC) is proposed by integrating the structural strength model of FT damage and the energy balance size effect model previously proposed by the author. Subsequently, parameters analysis of the EBM-FTC is conducted. Finally, the EBM-FTC is validated by using the experimental results of the size effect of different quasi-brittle materials under FT cycles. Furthermore, by analyzing the EBM-FTC parameter values determined through fitting for experimental results of different quasi-brittle materials, the EBM-FTC is simplified. The results show that: the structural strength model of FT damage is capable of precisely describe the nonlinear characteristics between the quasi-brittle materials strength of the whole specimen and FT cycles. The EBM-FTC can describe the novel size effect phenomenon mentioned above. This proves that it can also reflect the underlying mechanism of the coupling effect of specimen size and FT cycles on the strength of different quasi-brittle materials. The minimum determination coefficients of EBM-FTC is 0.845 2, indicating high model accuracy. The minimum coefficient of determination R² of the simplified EBM-FTC is 0.841 0, indicating that the simplified EBM-FTC still has high accuracy and the simplification is reasonable. Parameters analysis of the EBM-FTC indicates that the decreased strength and increased thickness of the damaged surface layer caused by FT cycles are the cause of the ascending size effect; the descending size effect occurs because the volume ratio of the damaged surface layer is negligible compared to the undamaged interior region; The ascending-descending size effect is governed by both the damaged surface layer and the undamaged interior region. EBM-FTC has achieved a quantitative characterization of the coupled influence of FT cycles and size on the strength of quasi-brittle materials. It can be directly applied to the design of the minimum safe size of quasi-brittle materials components in cold regions under known service FT cycles, or to infer the freeze-thaw durability threshold based on the design size.