In the research on liquid lithium, the corrosion compatibility of the structure material in the fusion blanket is the issue of most concern. A Chinese low-active ferritic steel (CLF-1) is a candidate liquid lithium blanket structure material. Thus, it is necessary to investigate its corrosion behavior in liquid lithium. In our work, CLF-1 samples were exposed to liquid lithium corrosion at 500 °C for 500 h. The variation in the chemical composition was analyzed by the laser-induced breakdown spectroscopy (LIBS) technique to understand the corrosion process of mass transfer and diffusion. During the LIBS depth profile analysis, we found that the influence of the matrix effect could not be neglected in the surface. It is caused by the non-uniform surface microstructure, which induces a fluctuation of the spectral intensity. An improved internal standard method is applied to the data processing to eliminate this interference. The content distribution is obtained in the corroded layer by selecting the neutral and ionized Fe atom as internal standard. From the variation trends of the relative concentrations between elements it is deduced that the relationship of relative mass loss during the matrix elements is Fe > Cr > V ≈ Mn.