Trissolcuss grandis Thomson, is an important egg parasitoid of Eurygaster integriceps Puton that can control its population in wheat and barley fields. Despite valuable results from previous studies, the thermal development of T. grandis over a wide range of temperatures had not been elucidated completely. This study was conducted to evaluate the thermal effect on the development of T. grandis using Sunn pest eggs as hosts in a wide range of temperatures (12.5 to 40 ±0.5℃, 65 ± 5% RH., and a photoperiod of 16L:8D h) in the laboratory condition. The development times of the immature stage (Egg-Adult) of T. grandis decreased with increasing temperatures up to 35 ºC for both sexes. Patterns of temperature-dependent development times of the immature stage of females and males (i.e. emergence of females and males of T. grandis adults) were modeled and simulated with linear and nonlinear regression analyses. The estimated low-threshold temperatures (Tb) were 10.61 and 10.62 ºC for females and males, respectively. Thermal constants (k) of the immature stage of females and males were 179.85 and 161.03 degree-days (DD), respectively. Stage transition models for females and males adults of T. grandis were constructed using two basic components of nonlinear development rate (modified Sharpe & DeMichele model function) and distribution models (two-parameter Weibull function) to simulate the proportion of individuals shifted from egg to adult. These models will be useful in building a T. grandis population model that will describe its seasonal occurrence pattern and population dynamics under various wheat and barley fields and optimize environmental conditions in mass rearing.