The aeroacoustics level is one of the most important criterions for civil aircraft design. The slat noise is a dominating noise component during the aircraft landing. In this paper, the numerical simulation research of the slat noise frequency characteristic aiming to different angle of attack and blunt/ sharp main trailing edge was done by solving the unlinear disturbance equation in two dimensional. The results show that the unsteady vorticity in the slat cove causes the noise . As the angle of attack decreased, the strength of the unsteady vorticity increased with the extent broadening and radiate more noise. It could be seen from the unsteady acoustic field and frequency characteristic that the slat noise is a kind of dipole source with broadband characteristic. The dominating noise component arose in low and mid frequency. The noise amplitude decreased as the frequency increased. The physics and frequency characteristic is well captured by numerical simulation which makes a good foundation for noise control.