The effect of electric field enhancement on laser-induced damage morphology of multi-layer dielectric gratings was investigated. Electric field distribution was calculated by using the Fourier mode method. Numerical treatment shows that the peak electric field occurs at the groove edge opposite to the incident direction by nearly a magnitude of two. Laser-induced damage threshold of 6.61 J/cm2 was obtained for 12 ns pulses at 1 064 nm with TE mode and 51.2° incident. Scanning electron microscopy (SEM) of damage morphology shows that the initial damage occurs from the place where the electric filed is strongly enhanced.