In this study, we systematically investigate the ultrafast spin dynamics and underlying physical mechanisms of Pt/CoFeB/Ta/SiO₂ ferromagnetic heterostructures at room temperature by using a femtosecond laser-based dual-pump optical pump–terahertz emission (OPTE) spectroscopy combined with the microscopic three-temperature model (M3TM). This integrated approach enables the qualitative characterization and quantitative analysis of ultrafast magnetization dynamics, which serves as a simple and efficient strategy for probing spin–charge coupling in magnetic heterostructures. The time-resolved OPTE measurements clearly resolve a three-stage ultrafast magnetization evolution process: an ultrafast demagnetization within a sub-0.2 ps timescale, followed by two distinguishable magnetization recovery stages dominated by electron–phonon interaction and spin–phonon interaction, respectively. Quantitative analysis demonstrates that the demagnetization time is nearly independent of the control pump fluence, and is significantly shorter than that of single-layer Fe films in our previous work. This accelerated demagnetization is attributed to the introduction of Ta and Pt nonmagnetic layers, which strongly enhance the spin–orbit coupling and promote efficient interlayer spin transport and angular momentum transfer. Moreover, increasing the pump fluence intensifies spin fluctuations, reduces the transient magnetic anisotropy, and thus slows down the spin–phonon relaxation process. By quantitatively fitting the experimental dynamics with the M3TM, we successfully extract the key kinetic parameters including the electron–phonon coupling constant and lattice relaxation time. Both parameters show a monotonic increase with rising pump fluence, revealing a higher efficiency of energy transfer from the electronic subsystem to the lattice subsystem under stronger photoexcitation. These results explicitly highlight the crucial role of interlayer angular momentum transport in ultrafast demagnetization dynamics. This study not only deepens the fundamental understanding of ultrafast spin and charge transport mechanisms in ferromagnetic heterostructures, but also provides essential experimental benchmarks and theoretical guidance for the design and optimization of high-performance magneto-optical storage devices and terahertz emission devices.