Abstract The compatibility of the mechanical properties of low-modulus cement and asphalt mortar (CAM) and repair materials was studied using the four-point bending test method. According to the bearing characteristics of CAMs, a four-point bending fatigue test was further developed to evaluate the compatibility of this material with the repair material. With the help of a finite element model, the effect of the difference in the modulus of the substrate mortar and the repair mortar on the stress and strain distribution of a composite sample was studied. The results indicated that the CAM compatibility criteria with repair materials were different from those of the concrete repair system. The difference in the moduli of the substrate mortar and repair mortar determined the loading transfer efficiency and failure mode, which mainly influenced the compatibility of the mechanical properties. The repair materials were compatible with substrate CA mortar when its modulus was approximately 0.75–1.28 times the substrate mortar modulus according to the experimental results. The four-point fatigue test met the requirements of the bearing characteristics of the CA mortar and the present quantitative experimental results, which provide supplementary information for compatibility evaluation.