Abstract: Urban form is a key to understanding the spatial characteristics and historical evolution of old towns along regional transportation corridors. The ancient transportation fortress, as special type of small town, and a node and hub with multiple function was used to play an important role in enriching the understanding towards the ancient Silk Road and contemporary 'Belt and Road'. This paper selects the Jimingyi in Zhangjiakou City along the 'Northern Grassland Silk Road' as case study, constructs a 3D model through drones and tilt photography technology. It identifies the spatial elements such as town spatial layout, town function, and street and courtyards form. First, based on the 3D digital spatial model, it finds that the urban spatial pattern is almost keep still and do not change much. Second, by method of machine learning, it finds that the functions of zones within city are dramatically to residential use. It reflects the decay of transportation function with the decline of the routes of trading corridor in late Qing Dynasty. Third, in aspect of streets and lanes within town, more details in the model show that the buildings inside some courtyards are abandoned and walls are collapsed. This paper provides a low-cost, quick and efficient way to obtain urban form elements through drone and 3D modeling technology. It plays a direct role in presenting the urban form analysis to small towns. The application of this paper is to other similar small cities and towns along transportation corridor lies in that it will provide policy implications for improving the new technology supported urban planning and design along transportation corridor.