Abstract: In order to study the effect of the defects on damage threshold of the surface, we modeled a classical three-dimension defect which is similar to the circular cone protuberance and calculated the electric field around this kind of defects by finite-difference method. Based on the field effect theory we calculated the damage thresholds of surfaces with different size defects. It can be got that the electric fields were amplified obviously, which directly leads to lower damage thresholds. The damage threshold increases as incident wavelength increases and the height of defect decreases. The reduction of damage threshold caused by defect decreases first and then increases with the pulse increasing. The damage threshold owns a minimum at 1.80 ps and 15.80 ps when the wavelength is respectively 351 nm and 1064 nm.