In the positioning process of aerial cameras with large inclination angles, the influence of height error in the earth ellipsoid model can be effectively solved with the help of a digital elevation model (DEM). This is very important for obtaining accurate ground coordinates, especially elevation. Firstly, the orientation of the line-of-sight angle in the geographic coordinate system is solved by transforming homogeneous coordinates according to the position and attitude information of the carrier aircraft and the frame angle information of the aerial camera, and then the longitude and latitude of the target point are determined by a digital elevation model. To overcome the tedious nature of calculating target elevation and the non-convergence in the imaging process, a fast iterative method is proposed to iterate over the target elevation’s value. The difference between the light elevation of the visual axis and the ground elevation is calculated by halving the target elevation. The median elevation difference is calculated iteratively until it is less than a certain threshold. Finally, Monte Carlo analysis was used to analyze the error terms in the whole imaging process. When the convergence threshold is 1/10 DEM in grid accuracy, the iteration efficiency increases by 45.5% and the convergence speed is greatly improved. Through the calculation of the digital elevation model, when the flight height is 15,409 meters and the camera frame’s angle is greater than 74°, a mountainous area’s target circular error probability is less than 200 m which meets the real engineering needs.