Abstract: According to effect of the main diffusion process parameters on mirror pure iron surface roughness in the diffusion bonding processing of precision parts, 99.99% pure iron was used to study the effect of heating temperature and holding time on its surface roughness. Experimental results showed that at the temperature lower than 550℃ and holding time of an hour, the temperature had little effect on the iron surface roughness, but its effect had the increasing trend within 10 nm. At the temperature higher than 550℃, pure iron surface roughness increases slowly, until at 912℃ allotropic transformation of iron occurs, surface roughness change suddenly from original several nanometers to 700 nm. At 400℃ and holding time from 60 to 240 min, surface roughnessJP2changes little, which indicates that the holding time has few influence of surface roughness at 400℃.