Recently, band-splitting associated with spin polarization at K- and K′-points of the Brillouin zone has been found in centrosymmetric transition metal dichalcogenide materials. This discovery offers a possibility on centrosymmetric crystals for potential valleytronic applications. However, the origin of the band-splitting and the spin polarization in multilayer and bulk transition metal dichalcogenides remains unclear as the interlayer coupling should play a role when compared with that in monolayers. Here, by performing spin- and angle-resolved photoemission spectroscopy in bulk 2H-WSe2 at variable temperatures, we have quantitatively established contributions of the intralayer spin–orbit coupling and interlayer coupling. While the strength of the intralayer spin–orbit coupling is determined to be 450 meV, independent of the temperature, the strength of the interlayer coupling is found to increase from 68 to 172 meV as the temperature decreases from 300 to 80 K. This is also accompanied by an increase in the total band-splitting and a decrease in the spin polarization. This work reveals the micro-mechanism of spin and interlayer interaction in centrosymmetric materials, which provides a basis for the development of next-generation energy-efficient valleytronic devices.