In present study, aiming to the temporal and spatial evolutional characteristics of SSD beam focal spots and based on the optical imaging system of a streak camera, we carry out the beam test experiment with time resolution on the high-power laser device. Experiments demonstrate the influence of SSD beam control parameters on the dynamic evolutional characteristics of focal spots. The focal spots along the SSD scanning direction have typical CPP shaped speckle patterns. The dynamic evolutional modes presented by different modulation frequencies are different. The overall spatial-temporal distribution of intensity modulated by high frequency is more uniform, and a better smoothing effect can be achieved in short smoothing time. The spatial distribution and temporal evolution of the focal spot intensity in the vertical SSD sweep direction become very chaotic, showing the specific differences of SSD beams in two-dimensional space. The focal spot of the SSD beam has strong amplitude modulation, and the modulation has an obvious regional effect. Modulation depth is generally related to the SSD beam control parameters. Our results provide a better understanding of the dynamic evolution of the spot details of SSD beams, which can be combined with the mechanism analysis of LPI to support the optimization of SSD smoothing performances. The inconsistency of SSD beams in two dimensions can be used to optimize the sweeping direction of SSD, and the modulation structure of SSD beams can assist in the selection of modulation frequencies. An accurate description of focal characteristics provides important boundary conditions for optimizing the location of focal trajectory points.