The self-absorption of copper alloy plasma spectrum was studied by using 532 nm laser (pulse width of 8 ns) under the laser energy of 100, 80, 60 and 40 mJ. The effects at low ambient pressure on the self-absorption and spectral characteristics of copper alloy plasma were studied under the laser energy of 100 and 40 mJ. The research showed that the characteristic line (Cu Ⅰ 324.754 nm) has a serious self-absorption at standard atmospheric pressure, and the degree of self-absorption reduced with the decrease of laser energy. By reducing the environmental pressure properly, the degree of self-absorption greatly reduced, the SBR(Signal-to-Back Ratio) increased, and the self-absorption phenomenone liminated under a certain low pressure. Under the pressure of 5.0×104 Pa, the SBR under two laser energy reached its maximum value, which were 8.90 and 8.66 respectively, 11.23 and 12.62 times higher than the SBR at normal pressure, and the RSD (Relative Standard Deviation) were 2.9%, 1.3% at present. The spectral widths of two laser energy decreased rapidly with the decrease of ambient pressure. The spectral widths were 0.08 and 0.06 nm at the pressure of 5.0×104 Pa, which were 19% and 20% with the value of widths under normal pressurere spectively. The results showed that sensitivity and precision in spectral analysis can be significantly improved under low-pressure. It indicates that to select the element sensitive spectral line as analysis line is possible when analyzing higher content elements, and provides an effective method for the determination of high content elements in material accurately by LIBS.