The altitude information extracted from a single remote sensing image can be applied to detect the natural disaster, such as landslide or mud-rock flow. An approach based on dark channel prior was proposed for the altitude extraction from a single remote sensing image, which considers the influence of shadow. The approach was based on dark channel prior, and meanwhile a solution to overcome the effect of mountain shadow was given. The quantitative and qualitative analysis of a large number of mountain remote sensing images demonstrates that the proposed algorithm can obtain the accurate relative altitude information. In conclusion, the improved algorithm is effective for the extraction of the relative altitude from single remote sensing image of mountain with shadows.