Background As information technology has advanced and been popularized, open pit mining has rapidly developed toward integration and digitization. The three-dimensional reconstruction technology has been successfully applied to geological reconstruction and modeling of surface scenes in open pit mines. However, an integrated modeling method for surface and underground mine sites has not been reported. Methods In this study, we propose an integrated modeling method for open pit mines that fuses a real scene on the surface with an underground geological model. Based on oblique photography, a real-scene model was established on the surface. Based on the surface-stitching method proposed, the upper and lower surfaces and sides of the model were constructed in stages to construct a complete underground three-dimensional geological model, and the aboveground and underground models were registered together to build an integrated open pit mine model. Results The oblique photography method used reconstructed a surface model of an open pit mine using a real scene. The surface-stitching algorithm proposed was compared with the ball-pivoting and Poisson algorithms, and the integrity of the reconstructed model was markedly superior to that of the other two reconstruction methods. In addition, the surface-stitching algorithm was applied to the reconstruction of different formation models and showed good stability and reconstruction efficiency. Finally, the aboveground and underground models were accurately fitted after registration to form an integrated model. Conclusions The proposed method can efficiently establish an integrated open pit model. Based on the integrated model, an open pit auxiliary planning system was designed and realized. It supports the functions of mining planning and output calculation, assists users in mining planning and operation management, and improves production efficiency and management levels.