Abstract: In order to solve the significant shielding effect of light-induced plasma on laser during high-power diode laser processing, with the help of the mathematical model of electron density of light-induced plasma and ABCD matrix algorithm, the shielding effect of light-induced plasma was studied from the view of absorption and refraction based on a diode laser processing system with wavelength of 976nm, spot size of 0.5mm1mm and the maximum power of 4kW. The results showed that laser beam shielding effect is mainly due to refraction effect of light-induced plasma under the condition of electron density ne1.01018/cm3. Laser beam shielding effect changes laser beam shape, i.e., making the laser focus down-shift, enlarging the spot and making the laser energy density smaller. The effect of induced-laser plasma is similar to a negative lens with non-linear gradient refractive index.