In order to develop a high sensitive and low cost metal elements analysis method for aqueous sample, an ultrasonic nebulizer assisted spark induced breakdown spectroscopy (UN-SIBS) system is established, where an ultrasonic nebulizer is employed to transform the bulk liquid sample into aerosol composed by intensive droplets. And a high tension coil and a couple of electrodes are combined to induce the plasma. The spectra emitted are collected to analysis the metal elements in the aqueous samples. Based on the experimental system, the features of emission spectra are studied. The electron density and electron temperature are calculated to understand the physics characteristic of the plasma in UN-SIBS experiments. Samples of different concentration of lead are analyzed by UN-SIBS method to make clear of the relationship between concentration and the peak intensity of the heavy metal element Pb. Besides, the atomic line of lead at 261.37 nm detected by the sample with the concentration of 2.07 ppt could be easily distinguished which is better than the LOD reported in references. The aqueous samples with calcium, as a lower activity metal element, are also studied. At last, the possible mechanism is discussed according to the experimental results.