The behavior and mechanism of crack initiation and coalescence of S-shaped fissure are investigated in the study to shed more light on the failure characteristics of non-straight fissures. The uniaxial tensile tests with 3D-printed samples and numerical simulations are carried out to study the influence of different geometric parameters of S-shaped fissure, including the inclination angle β and effective curvature A/c. The crack coalescence of an S-shaped fissure is observed to occur exclusively through tensile cracks, while the tip cracking and non-tip cracking patterns of S-shaped fissures can be identified based on the crack initiation position. It is found that the inclination angle and effective curvature have a substantial influence on the failure mode of the S-shaped fissure. Based on experimental results, extensive numerical simulations are performed to predict the cracking patterns, e.g., tip cracking/non-tip cracking. A reasonably effective, quick criteria approach for identifying the coalescence patterns in terms of parameters A/c-β for S-shaped fissures under uniaxial tension is derived based on vast numerical calculations. The current study yields a favorable demonstration of the application of 3D printing technology in adept arbitrary geometry formation.