Gel time is an important property of functional hydrogels. In order to accurately determine the gel time of hydrogels, traditional rotational rheometer and diffusion spectrometer (DWS) were used to analyze the dynamics of structural changes in the process of gel. The results show that the rotational rheometer can continuously measure the macro mechanical properties in the process of gel, and the modulus change curve reflects the instantaneous change of gel system. However, the external force exerted on the sample by the rotary rheometer during the measurement process leads to a certain degree of lag in the gel process, and the external force will destroy the sample after crosslinking and curing, resulting in the inability to continue to measure subsequent changes. DWS determines the microstructure changes by detecting the diffusion of the sample to light. Without external stress interference to the sample, it can obtain the dynamic information of gel behavior in the undisturbed state, and further track the microstructure changes after the crosslinking and curing of the hydrogel.