The coherent CO₂ laser imaging system has high resolution, strong anti-interference and 3D imaging, but its imagery is usually affected by speckle noise, imaging resolution descend. It's important to study on suppressing speckle algorithms for this system. In the paper, three common algorithms——median filtering, homomorphic mean filtering, and Lee filtering were introduced and used in suppressing speckle in coherent pulse CO₂ laser imaging system. Then these algorithms were compared. The results show that non-iterative Lee filtering with small windows is better. The speckle noises are suppressed clearly, and image edges are maintained.