Traditional ecological suitability evaluation methods based on current land use status have their limitation in supporting development decision for urban construction land in rapid urban-expansion regions. This article first proposed the concept and method of potential ecological suitability evaluation of urban construction land. The method highlights the predicted future urban land-use distribution that is regarded as an important factor in the ecological suitability evaluation framework, and generates the evaluation result that is suitable for future planning and decision making of urban construction land. This study took Baoshan District, Shanghai Municipality, China as the study area and presented the spatial distribution of ecological suitability of urban construction land in 2050 under the background of urban expansion. The result was compared with the traditional ecological suitability evaluation results. The comparison revealed that potential ecological suitability evaluation can effectively reduce the high overlaps of the lands unsuitable or moderately unsuitable to be developed and the future urban buildup areas (reducing the overlap from 9.74% and 22.7% to 0.0% and 14.5%). It can match the urban development boundary planning and ecological space planning better and highlights the key protected ecological regions in future development. The case study proved the soundness and effectiveness of the new evaluation method, which can provide better decision supporting for ecological urban planning under the background of urban expansion.