The emergence of transition metal dichalcogenides as two-dimensional electronic materials has stimulated proposals of novel electronic and photonic devices based on the heterostructures of transition metal dichalcogenides (TMDs). The band alignment for TMD heterostructures is practically important for applications. We examined the feasibility of Electron Affinity Rule (EAR) on TMD heterojunction band alignment by stand-alone X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). Our results suggest that the EAR can successfully predict the band alignment of TMD heterostructures.