Traditional infrared thermography (IRT) techniques can only provide two-dimensional (2D) projections of surface temperatures, and it is difficult to intuitively present the surface profile of the three-dimensional (3D) structure and the spatial distribution of the internal defects. In this paper, a low cost, high efficiency and high precision photothermal 3D tomography technology was proposed by combing 3D thermography and infrared tomography for the first time. Specifically, this paper abandoned additional 3D sensors and complex motion systems such as robotic arms and scanning platforms. Differently, it utilized a galvanometer to deflect laser for line structure light scanning, and captured the thermal stripes generated on the structural surface using an infrared camera, and then realized the highly efficient 3D reconstruction; moreover, this work introduced undersampling strategy into photothermal coherence tomography (PCT) technology to enhance the ranging depth, and the ranging results were transmitted to the 3D coordinate system, so as to realize the photothermal 3D tomography. Through the detection experiments of metal additive manufacturing parts, it was shown that the proposed method could reconstruct the 3D contour of the specimen, and identified the first heterogeneous interface below the surface of the specimen.