Due to the uneven intensity distribution of Gaussian pulsed laser beam, traditional laser-induced breakdown spectroscopy (LIBS) system has poor spectral signal stability, and the detection sensitivity for trace elements is low. To improve the analytical performance of LIBS, a combination of spherical lens and cylindrical lens is used to focus the laser beam to ablate the alloy steel sample to generate plasma in this study. The research results show that a more uniform ablation crater morphology is formed by adding a cylindrical focusing lens to the experimental system, which to some extent avoids the adverse influence of the "pointed conical" ablation crater formed by Gaussian beam excitation on the spectral signal in traditional systems, and a more stable plasma radiation spectrum is obtained. Compared with the traditional LIBS, the signal stability of characteristic spectral line intensity and background intensity in this work has increased by 24.7%-36.67% and 43.75%-57.7% respectively, and the stability of plasma temperature and electron density has increased by ~10%. Furthermore, three trace elements, Mn, Cr and Ni, in alloy steel are quantitatively analyzed using the internal standard method. The result shows that the use of cylindrical lens focusing improves the detection sensitivity of elements, and the limit of detection (LOD) of elements is reduced by 1.15-3.01 times.