In order to suppress speckle noise during holographic recording, a coherence method by reducing the coherent light source was used, and the theoretical analysis and experimental verification were performed. A rotating binary wave plate was used for depolarization, and 70 holograms were recorded in 10s for average noise reduction. At the same time, ground glass was used for spatial decoherence of the coherent light, which reduces the coherence of the light source and thus the speckle noise. The reconstructed image with the temporal depolarization operation alone was compared with the reconstructed image with the spatial depolarization operation alone, and the reconstructed image combining the two. The feasibility of the proposed method was verified by experiments, and several methods were confirmed by analyzing the frequency spectrum comparison. The signal-to-noise ratio was used to directly confirm the effectiveness of several methods. The experimental results show that the combination of time and space depolarization has obvious advantages in suppressing speckle noise. The signal-to-noise ratio of the reconstructed image with spatial depolarization is 0.4459, the reconstructed image with time depolarization is 1.5155, and the combined image with time depolarization is 1.7162. The method of time decrement and space decrement stack is used to suppress the coherent noise effectively. This experiment provides an effective method for the study of speckle noise caused by the over-high coherence of light source in the process of digital holographic imaging.