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The self-absorption effect is one of the main factors affecting the quantitative analysis accuracy of laser-induced breakdown spectroscopy (LIBS). In this paper, the self-absorption effects of laser-induced 7050 aluminum alloy plasma under different pressures in air, argon (Ar) and nitrogen (N2) have been studied. Compared with air and N2, Ar significantly enhances the spectral signal. Furthermore, the spectral self-absorption coefficient (SA) is calculated to quantify the degree of self-absorption. And the influence of gas species and gas pressure on self-absorption is analyzed. In addition, it is found that the spectral intensity fluctuates with the change of pressure of three gases. And it can be seen that the fluctuation of spectral intensity with pressure is eliminated after correcting, which indicates that the self-absorption leads to the fluctuation of spectral intensity under different pressure. The analysis shows that the evolution of optical thin spectral lines with pressure in different gases is mainly determined by the gas properties and the competition between plasma confinement and Rayleigh-Taylor instability.