The essence of coal-rock dynamic disasters is the instantaneous instability that occurs when the coal-rock combination system reaches its strength limit. The differing mechanical properties of coal and rock lead to mismatching deformation within the combination, thereby altering the mechanical characteristics of the coal-rock body under combination structures. Consequently, studying the mismatching horizontal deformation of coal-rock combinations is significant for the prevention and control of coal-rock dynamic disasters. To investigate the mismatching horizontal deformation characteristics of primary coal-rock combinations, this study conducted uniaxial and conventional triaxial loading experiments on primary coal-rock combinations to obtain their strength and horizontal deformation characteristics. Subsequently, numerical simulations were performed to analyze the factors influencing the horizontal deformation of primary coal-rock combinations, ultimately leading to the construction of a horizontal deformation distribution model for primary coal-rock combinations. The research results indicate that due to the influence of the coal-rock interface, the primary coal-rock combinations exhibit continuous and smooth mismatching horizontal deformation under loading conditions, with the magnitude of deformation ordered as coal > interface > rock. The influence of the interface on the horizontal deformation of the coal-rock body does not suddenly vanish; rather, it gradually diminishes with increasing distance from the interface, becoming negligible at approximately 48% of the model’s lateral dimensions. A horizontal deformation mismatch distribution model for primary coal-rock combinations was established based on the Sigmoid function, and the key parameter b in the model was obtained through fitting with numerical simulation results. The reliability of the model was subsequently validated through experimental results. The findings of this study provide a basis for further research on the mechanical properties and deformation characteristics of coal-rock combinations.