The significant challenges that urban design faces when moving forward into this new digital era involve the increasingly massive and complex projects that must be analyzed and developed.The need for efficient analysis tools and rational design methods represent ongoing concerns, while practicable and maneuverable applications rather than experimental studies are scarce.This research implemented a framework of digital description and genera-tive grammar of block form from the perspective of block morphological complexity.The im-plemented framework was tested in an urban design practice.First, this study adapted the hierarchical structure and access structure theory to analyze the spatial form of target blocks.The characteristics of blocks case samples in Nanjing are extracted as text descriptions.Sec-ond, the relevant composition patterns and parameters were employed as features for classi-fication and were converted into procedural rules.With the top-down control by rules and bottom-up generation by shape grammar in CityEngine, the texture of the block can be gener-ated as close to the actual block as possible.Furthermore, in a real urban design case located in Nanjing, this work applies the method to construct a three-dimensional scene quickly and accurately.After integrating design factors such as an environment, transportation, and vision and summarizing the intentions of blocks and buildings in corresponding functions and control indexes, the initial generation plan was built by applying the obtained characteristics and pro-cedural rules in specific shape grammar.Finally, designers can adjust the result in detail by employing real-time calculation and interactive operation.