The effect of flaw filling material on the deformation and failure behaviour of 3D printed rock-like Brazilian discs with pre-existing flaws is investigated by quasi-static compressive loading test combined with digital image correlation (DIC) technique. In particular, a number of specimens with various flaw and bridge inclination angles and overlapping features are designed by computer aided design (CAD) and 3D printed. Crack initiation and propagation in the loaded specimens are studied and coalescence types of these flaws are identified by DIC analysis. The results indicate that filling material imposes strong impacts on the deformation behaviour of specimens and the resulting crack patterns are different from those with open flaws. It is revealed that filling the flaws with gypsum and clay mixture improves the strength characteristics of the specimens with significantly enhanced peak loads. Furthermore, DIC results indicate that in the single filled flaws inclined at 45°, 60° and 75° normal to the loading direction, the shear cracking first develops in the filling and then tensile cracks appear from the flaw tips. It is observed that the filled specimens develop much larger fracture process zone prior to the peak load. Moreover, when the specimens develop a crack inside the fillings, the enhancement of the peak load is remarkably larger than that of the filled specimens without cracking in the fillings. Overall this study has demonstrated not only the advantages of 3D printing combined with DIC method in rock deformation and crack study, but also the significant impacts of the flaw filling on the deformation and mechanical behaviour of rocklike material.