In this paper, a four-dimensional (4D) thermal imaging model containing three-dimensional spatial information and temperature information of objects is designed and developed. It is proposed to map and merge the high-precision threedimensional (3D) point cloud data obtained by structured light 3D reconstruction technology with the two-dimensional thermal image with temperature information (1D) taken by infrared (IR) camera. The spatial thermal imaging model has the advantages of high precision and fast reconstruction speed. At the same time, a calculation model for the emissivity of the object with uneven surface is presented. This emissivity calculation method shows that the emissivity of the measured object is related to the concave part, the surface area covering the concave part, and the emissivity of the surface coating of the measured object. By designing and manufacturing the concave shape measured object with high-temperature resistant sanding paint on the surface, the results show that the calculation method of the emissivity of the measured object suitable for the concave shape of the surface proposed in this paper requires less physical parameters than the traditional method, and the calculation accuracy is also guaranteed. Because the shape of the concave surface is usually irregular, its surface area measurement has become another problem. Here, we use the built 4D thermal image model reconstruction system to perform four-dimensional repair on the measured concave surface. The surface area of the selected surface is measured by means of mesh division and mesh area integral calculation. Substituting the surface area of the above concave surface into our emissivity calculation formula, we can also get better results.