Giant molecular clouds tend to join together in a larger structure called molecular cloud complex (MCC). In one way, MCC has an important role in linking the physical properties of Milky Way structures to those of other galaxies. In another way, it serves as the nest of massive star formation event. In this talk, I will discuss recent results from high-angular resolution and high sensitivity observations of Galactic MCCs in both of aspects of connecting to other galaxies and to massive star formation. The framework of connecting to other galaxies is based on the mutual scaling relations between mass, size, velocity dispersion and star formation rate. Whereas, for massive star formation, it is based on the influence of the large scale structure on star formation.