Scopula subpunctaria (Herrich-Schaeffer), is a significant insect pest affecting tea plantations in China; however, its thermal developmental characteristics remain inadequately understood. This study examined the immature developmental stages of S. subpunctaria under eight constant temperature regimes (13, 16, 19, 22, 25, 28, 31, and 33 °C) in controlled laboratory conditions. Results indicated an inverse relationship between temperature and the total duration of the immature stages (egg to pupa), with developmental time decreasing from 105.8 days at 13 °C to 29.3 days at 31 °C. Specifically, the developmental durations for eggs, larvae, and pupae ranged from 5.4 to 20.3 days, 15.4 to 52.3 days, and 8.1 to 33.3 days, respectively, in 13 °C to 31 °C temperature range. Using an ordinary linear model, the estimated lower developmental threshold temperatures were 8.61 °C for eggs, 8.40 °C for larvae, 9.39 °C for pupae, and 8.85 °C for the total immature stage, with corresponding thermal constants of 114.94, 302.11, 149.93, and 558.99 degree-days (DD), respectively. Comparative analysis of eleven nonlinear models revealed substantial variation in estimates of lower and upper temperature thresholds, while estimates of optimal temperatures showed minor differences. Based on statistical criteria and biological relevance, the Briere-2 model was selected to characterize egg development, the Lactin-1 model for larval development, and the Briere-1 model for pupal and total immature stages. Stage transition models for eggs, larvae, pupae, and the total immature period were constructed using a two-parameter Weibull function integrated with the respective nonlinear models. This study provides foundational insights into the thermal developmental characteristics of S. subpunctaria and offers predictive tools for forecasting stage-specific emergence in tea plantations.