Efficient spin-orbit torque (SOT) driven magnetization switching in thermally robust heterostructures with large perpendicular magnetic anisotropy (PMA) is crucial for the next-generation magnetic random access memory (MRAM). While β-W as a promising candidate due to its large spin Hall angle and high compatibility with CoFeB/MgO-based magnetic tunnel junctions tends to undergo a phase transition to α-W, which can significantly reduce spin Hall angle by high-temperature annealing. Here, we report that amorphous WTaB/CoFeB/MgO heterostructures grown by magnetron sputtering and annealed at temperatures up to 450 ℃, exhibit strong PMA with thermal stability and efficient SOT manipulation of magnetization states, primarily due to the addition of Boron (B). Structural characterizations via X-ray diffraction and cross-sectional high-resolution transmission electron microscopy demonstrate the amorphous nature of WTaB buffer layer and (001) orientated CoFeB/MgO stack after annealing. Magnetization measurement by vibrating sample magnetometry reveals an effective PMA field of the films as high as 350 mT, even after annealing at 450 ℃. Furthermore, the current-induced magnetization switching was achieved with a critical switching current density Jc as low as 2.4×1010 A·m^-2 under an assistant field of 200 mT, indicative of a lower current-switching threshold for WTaB layer compared with those of previously reported in β-Ta and β-W systems. The damping-like torque and field-like torque effective fields (H_DL and H_FL), as well as the spin Hall angle of amorphous WTaB, were determined through harmonic Hall voltage measurements. For initial magnetization-up state, H_DL and H_FL per unit current density were -8.2 mT/(10¹¹ A·m^-2) and -1.8 mT/(10¹¹ A·m^-2), respectively. While for the magnetization-down state, they were 7.6 mT/(10¹¹ A·m^-2) and -1.4 mT/(10¹¹ A·m^-2). The magnitude of H_FL is much smaller than that of H_DL, suggesting that a weak contribution from the interfacial Rashaba effect to the total SOT, with the bulk spin Hall effect in WTaB buffer being the dominant source. The spin Hall angle of WTaB was approximately -0.44, in agreement with the reported value in the in-plane magnetized systems measured by spin transfer torque-ferromagnetic resonance. Our work demonstrates that amorphous WTaB, as an efficient charge-to-spin conversion material, holds great potential for driving the development of low-power spintronic devices with perpendicular magnetization.