The slag sample is ablated by laser with the wavelength of 1064 nm. Some factors which influence the stability of signal are analyzed. The fluctuation of energy within ±2% has an unapparent influence on the stability of signal. The energy of reference laser has an unclear relationship with the intensity of signal spectrum. When the laser frequency is reduced to 4 Hz, the relative standard deviation of signal falls to about 10%. It is found that the intensity and stability of signal are the best when laser focus position is 3 mm below the surface of sample. It is demonstrated that the signals of smelt slag samples have better stabilities than thoes of grinded slag samples and different kinds of slags also have different signal stabilities. It is shown that the stability of signal from different ablated spots is better than that of the signal from the same ablated spot for atom lines, but there is no obvious distinction for ion lines.