：Thermal fracture is a common problem in engineering. Traditional studies mainly addressed surface crack propagation, with limited research on 3D internal crack propagation. This paper uses the 3D-ILC method to fabricate 3D internal cracks of different positions within semi-disc specimens. Physical experiments, numerical simulations and fracture morphology analysis were conducted on the propagation of 3D internal cracks under non-uniform temperature fields. The results indicate the following: 1) In physical experiment, different crack propagation modes were observed in group A at different heights, including “n-shaped” and “u-shaped” cracks, while group B formed the “s-shaped” cracks. 2) In numerical simulation, the crack propagation length and deflection angle for crack tips on both sides are different of the same specimen in group B. The K Ⅲ of the internal cracks in group B cannot be overlooked, consistent with the location of the “lance-like” fracture observed in the physical experiments. 3) In fracture morphology, group A cracks have smooth fracture surfaces, which are mode I-II mixed cracks, while group B cracks show lance-like fracture, considered mode I-II-Ⅲ mixed cracks. The results provide an experimental and theoretical basis for the study of 3D internal crack propagation patterns under non-uniform temperature fields.