Exploring the benefits of carbon sinks from the perspective of small-scale green spaces can provide more theoretical support for the development and research of future urban green and low-carbon spaces. By researching the existing green spaces in Xi’an, this study attempts to screen the plant species with high carbon fixation and low maintenance through calculation, explore the relationship scale between green spaces, plants, and carbon sinks, construct a typical plant community configuration model of “tree shrub + herbaceous community structure” “herbaceous community structure”, and summarize a plant landscape design method suitable for regional characteristics of urban carbon sink units. Analyzing the process of plant landscape construction based on the carbon sink unit of small-scale urban green spaces requires achieving a coupling between green spaces, plants, and carbon sinks. The methods and strategies of plant landscape design, which incorporate regional characteristics and promote efficient carbon sequestration, are proposed as an essential approach to achieving the urban “dual carbon” goals. Based on the current achievements in urban green space unit plant landscape construction, this paper organically combines urban small-scale green space construction with high carbon sink plant landscape design, aiming to provide new ideas for the construction of plant landscapes in urban small-scale carbon sink units.