Dammann grating is one kind of binary optical elements. We fabricated Dammann gratings in silica glass using femtosecond laser pulses at the wavelength of 800 nm with the repetition rate of 1 kHz. By using two-dimensional (2D) scanning system, we produced successfully 5*5 Dammann gratings for He-Ne laser with the wavelength of 632.8 nm. We selected suitable writing parameters to keep the length of the refractive index changed region as 160 microns across the grating. It makes the phase shift of the modulated region close to be 'pi'. The diffraction efficiency of the fabricated Dammann grating in our experiment reached to 56%, quite close to the theoretical value of 77%.