Dual-pulse laser-induced breakdown spectroscopy (DP-LIBS) is essential for highly sensitive trace element detection. Although various mechanisms have been proposed for its signal enhancement, further investigation is needed regarding plasma radiation fluorescence characteristics, spatial distribution of plasma temperature, and particle number density. This study developed a theoretical model based on laser ablation and two-dimensional axisymmetric fluid dynamics to simulate the spatiotemporal evolution of plasma generation and irradiance in aluminum-magnesium alloy under single-pulse LIBS and coaxial dual-pulse DP-LIBS conditions. We compared spectral line intensity enhancements at different pulse intervals and analyzed the spatial distribution of plasma temperature, particle number densities, and plasma shielding effects to clarify the signal enhancement mechanism of DP-LIBS. Results indicate that the increased particle number density and plasma temperature from the second laser beam primarily drive the enhanced plasma radiation signals, while plasma shielding occurs mainly at the target surface boundary layer. This study offers a vital theoretical foundation for experimental research and signal enhancement in DP-LIBS, aiding researchers in optimizing experimental device parameters efficiently.