In order to realize high spatial resolution elemental microanalysis, a gated signal amplifier is designed based on OPA 695 operational amplifier and is applied in weak signal detection in orthogonal dual-pulse laser-ablation laser-induced breakdown spectroscopy. This gated amplifier rejected the influence of strong electronic Bremsstrahlung emission successfully, and the weak atomic emission could be selectively amplified, thus the spectral analysis sensitivity and spatial resolution could be improved. Major aluminum and minor copper elements in an aluminum standard sample are analyzed experimentally. Under current experimental condition, the spatial resolution has been reached 0.9 and 1.2 μm while analyzing aluminum and copper, respectively. These spatial resolutions are significantly improved in comparison with 2.9 μm for aluminum and 6.2 μm for copper obtained experimentally without using this gated signal amplifier. This gated amplifier is low cost and is helpful for high sensitive detection of weak signal accompanied with strong and time-resolvable background.