Traditional Chinese private gardens (TCPGs) are a special type of seventeenth century landscaped architectural space that exhibit high levels of spatial complexity and variety, which are attributed to its patterns of spatial organisation. Sightline designs in these gardens are unique and ingenious. To date, only a few theories have tried to explain their spatial qualities from the perspective of visual analysis. However, there is a lack of formal mathematical analysis of sightline design in relation to the spatial organisation in TCPGs. To achieve this, the paper presents a study of sightline compensation analysis for a typical TCPG (the Humble Administrator’s Garden) using the semantic network method. The semantic network model is established on two levels—spatial accessibility and superimposed sightline. Results of this study suggests that sightline compensation forms the circular spatial structure that spreads outwards from core spaces, and composes the mathematically key spatial sequence of the Humble Administrator’s Garden. The effect of sightline compensation also expands and composes the spatial structure of the garden, which creates the effect of endless views within the garden. This study provides a new method for analysing and understanding contemporary landscape architecture design, which potentially benefits landscape architecture practitioners, students and educators.