Building a reasonable and feasible index system for Populus euphratica habitat evaluation in the Tarim River basin is important for social development, economic sustainable development, and ecological environmental protection and will provide a scientific basis for decision-making. Based on data for P. euphratica height and diameter at breast height (DBH), a model for a height-diameter coefficient was established. Quantitative analysis of the relationship between the height-diameter coefficient and DBH, age, response to habitat type, and analysis of the causes was conducted. The results showed that ① Based on the low-level landform (flood plain) habitat type, the index model simulated trends in the height-diameter coefficient of P. euphratica with changes in DBH. Response characteristics of simulated curves for different habitat types varied. The height-diameter coefficient of P. euphratica increased in different habitat types as the DBH decreased. ② With an increase in tree age, the height-diameter coefficient gradually decreased. ③ The height of P. euphratica under constant DBH conditions in the middle terrace, high terrace, and sand habitat types was equivalent to 70%, 42%, and 22%, respectively, of the height of P. euphratica in the floodplain-low terrace. ④ The growth environment of P. euphratica was better when the height-diameter coefficient was higher. Thus, the height-diameter coefficient of P. euphratica could be a sensitive indicator of P. euphratica habitat types. This study further enhanced the evaluation index system for forest habitat by using tree height and DBH model theory. It has implications to the merit of the ecology and forest mensuration theory system.