The refractive index-modulated grating, performed by line scan in fused silica with a femtosecond laser at wavelength of 810 nm and repetition rate of 1 kHz, were presented Dependence of the refractive index-modulation on femtosecond laser pulse energy, scan speed, spacing period, and scanning repetitions was investigated The refractive Index modulation reached to 3×10-3 after several scanning repetitions. It was revealed that the accumulation effect played a very important role in the formation of refractive index-modulated structures.