Currently, researchers employ LED targets combining with image thresholding method to address the issue that the visibility and resolution of structural surface characteristics decrease due to the influence of low-light environment, and finally induce the worse performance for the structural dynamic parameters measurement when using the vision-based technology. However, on the other hand, the complex ambient lighting and unfavorable weather in practical application will inevitably induce the negative effect for the vision-based measurement of the structural parameters. Therefore, in order to deal with this issue, a novel vision-based measurement method was proposed in this paper based on the iterative Otsu algorithm, in which the correct segmentation of the foreground spot and background image with the influence of strong light and fog interference can be realized by iteratively solving the image foreground threshold when combining with the iterative constraints of spot roundness and inter-frame area consistency, and fianlly the structural dynamic deflection can be obtained after collecting the spot center by the gray centroid algorithm. In this paper, the principle of the image thresholding segmentation based on the proposed iterative Otsu algorithm and the corresponding procedure for the structural displacement measurement were introduced at first. Subsequently, a cantilever beam specimen was employed to validate the feasibility and effectiveness of the proposed method, and finally the results demonstrate that the proposed method can realize the accurate identification of the structural dynamic deflection under low light conditions even with the influence of strong light and fog.