Addressing the issue of insufficient ecological performance during urbanization in the Western Loess Tableland Region and guided by the concept of Low Impact Development (LID), this study proposes a suitability and diversity design methodology for plant communities in bioretention facilities. The objective is to improve the synergistic benefits of regional biodiversity and stormwater management. Utilizing Weinan City, Shaanxi Province, as the study area, bioretention facility types were classified and their characteristic differences identified. Field investigations were conducted in representative ecological parks and LID projects within Weinan City. Selected quadrats were based on variations in bioretention facility characteristics and functional orientations. The biodiversity value of the bioretention facilities was quantified, with the Margalef richness index R reaching 3.694 and the Simpson diversity index D reaching 0.9049. Subsequently, matching optimization methods were employed for the optimized design of plant communities within these facilities. A dual-dimensional “habitat - diversity” plant community suitability design process applicable to bioretention facilities in the Western Loess Tableland Region was proposed. Bioretention facilities were categorized into 13 refined types, and corresponding suitability and diversity design patterns were established for each type. By synergistically considering biodiversity, habitat conditions, and bioretention facility types, an optimized suitability and diversity technical framework for bioretention facilities applicable to the Loess Tableland region was developed. This framework offers a scientific model and practical pathway for enhancing the ecological efficacy of LID in arid and semi-arid cities of Northwest China.