Abstract: A numerical investigation of an annular combustor in a transient state(from idle to maximum) was conducted with commercial software FLUENT by adding the UDF(user-defined function) subroutines.Temperature field was studied by comparing with traditional method(which used steady simulation at some discrete operation conditions to approximate the transient state).The results show that:(1)there are large differences between transient and steady simulation at corresponding operation condition,the outlet temperature distribution of steady simulation is higher than the transient simulation;(2) the time step is a critical factor affecting the accuracy of transient simulation,a small time step could account for the close interaction with flow filed parameters of different times;(3) a hysteresis phenomenon during the transient state exists at the averaged outlet temperature in relation to fuel-air ratio.