In this paper, by means of Cu(2+) converting to Cu, the sub-ppb detection of copper in aqueous solution was successfully achieved using laser-induced breakdown spectroscopy (LIBS), and the sensitivity was found depending on the voltage applied for the deposition. With increasing voltage, the minimum detectable concentration was significantly lowered, while the signal intensity instability was increased. In order to reduce the impact from the intensity fluctuation, an estimation method was developed to determine the copper concentration via comparing minimum detectable concentrations. The obtained results suggest this method is a potential way toward quantitative analysis.