Duplex stainless steel Z3CN20-09M serves as the predominant material for the primary pipeline within the first circuit of pressurized water reactor (PWR) nuclear power plants. Its aging grade estimation plays a crucial role in ensuring the safety of the nuclear island infrastructure. To achieve this goal, fiber-laser-based laser-induced breakdown spectroscopy (FL-LIBS) was introduced as the non-destructive and in-situ rapid detection technique for aging grade estimation. The spectral signals laser-induced plasma properties, and laser ablation processes of various Z3CN20-09M specimens with different aging grades were analyzed together with their microstructure and metallography. It was found that the spectral signal intensities of the matrix element (Fe) and the alloying element (Cr) increased with increasing aging grade, which was well explained by the increase in plasma temperature and ablation mass. Most importantly, reliable linear relationships were obtained between the signal intensity ratios of Fe Ⅱ/Fe Ⅰ, Cr Ⅱ/Cr Ⅰ, and Fe Ⅰ/Cr Ⅰ, to the aging grades, with the coefficient of determination (R2) ranging from 0.94 to 0.99. These results demonstrate that FL-LIBS is a feasible method for aging grade estimation of the Z3CN20-09M from nuclear power plants.