G-quadruplex structures of nucleic acids have been demonstrated to be widely existed in the genomes of prokaryotes and eukaryotes, meanwhile, involved in many biological processes, such as gene replication and recombination, telomere elongation, regulation of genetic expression, etc. Studying the interactions between G-quadruplex and ligands, such as Telomestatin, TMPyP4, BRACO-19, RHPS4, contributes to understand the roles of G-quadruplex and the corresponding mechanisms in biological processes. The research relies on a variety of analytical methods. Biochemical methods includes DMS footprinting, EMSA and DNA polymerase stop assay, and spectroscopy methods, such as circular dichroism, fluorescence spectrum, fluorescence resonance energy transfer, nuclear magnetic resonance and X-ray crystal diffraction. In addition, surface plasma resonance, electrospray ionization mass spectrometry and capillary electrophoresis are also included. This paper reviews the ligands targeting G-quadruplex and methods mentioned above for characterizing G-quadruplex's structures and interactions with ligands.