Abstract: Based on the principle of probe beam deflection,the ablation thresholds of three copper samples with different roughness are measured in moist and dry environment.The results show that,in the two kinds of environment,the larger the roughness,the lower the ablation threshold.When the roughness and the pump energy fluence are all equal,the ablation threshold is lower in the moist environment than in the dry environment.This phenomenon indicates that the rough and moist surface has big absorption coefficient to pump energy,which can be proved by the different transit time in the case of the same pump energy fluence.