The time-frequency characteristics of the transient response of dynamic gratings in erbium-doped fiber are different from stable gratings, which make it has great application value in the fields of fiber laser and optical fiber sensing. In consideration of the time domain characteristics, a time domain response model was built, which was based on metastable Er<sup>3+</sup> population rate equation and light field transmission equation. The model simulated the process of establishing dynamic gratings in erbium-doped fiber with time sequence. And the theoretical results showed that the formation time of the dynamic grating gets shorter with higher pump power and shorter Erbium-doped fiber length within the effective length limits, which was consistent with the experimental results obtained by the so called “Strong light and weak light alternation” method except that the measured formation time decay ranges obviously migrated to lower pump power relative to the theoretical results. In consideration of the frequency domain characteristics, the transient two-wave mixing process was approximately simulated by using four-wave mixing equation. The transient reflectance spectra obtained through numerical calculation reflected the evolution rule of the dynamic gratings, which were coincident with the experimental results gotten by the rapid optical frequency modulation method. Under the condition of 1.8m Erbium-doped fiber, the experimental results showed that the turning saturated pump light power from the absorption type dynamic gratings to the gain type ones is about 0.05mW, the maximum relative reflectance variation of the gain dynamic gratings (3%) is 3 times of the absorption types. The measurement results have important references to the practical application of Erbium-doped fiber dynamic gratings.