Grouting is commonly used to fill rock joints to provide reinforcement in geotechnical engineering. Understanding the fracture behavior of grouted rock joints depends on the characterization of infilled rock joints. In this work, mortar-filled rocks with grooved granite joints an inclination of 45° and infilling mortar layer between granite joints were simulated and a pre-existing cracks were assumed in mortar layers. Uniaxial compressive tests were performed on 20 specimens with different initial crack lengths a. Mix mode I-II fracture occurred in joints due to compression-shear condition. Peak load Pmax and fracture energy G0 were determined based on experimental load-deformation curves. The obtained results showed that both peak load Pmax and specific volume fracture energy Gf- V were observed to decrease with increasing initial crack length a. A simple bilinear distribution of local volume fracture energy gf-V was assumed to evaluate the effect of front boundary on specific volume fracture energy Gf- V to obtain the size-independent real fracture parameter of mortar-filled rock joints GF-V. Experimental results were also obtained by the established front boundary effect. It was observed that volume fracture energy and front boundary zone length were GF - V = 1.7 N/mm2 a* = 17.5 mm, respectively, which were consistent with experimental observations.