Hadrons, including mesons and baryons, are the smallest units that can be separated from matter and have been observed to have internal structures. Searching for new hadronic states and exploring their internal quark gluon structure is a cross cutting frontier topic of common concern in particle physics and medium to high energy nuclear physics. In recent years, more and more exotic hadronic states beyond the expectation of the classical Quark model have been observed experimentally. Although there are various explanations for their nature, these exotic hadron states can basically be explained as multi-quark hadronic molecular states. For hadrons that met the expectations of the Quark model in the past, such as protons, there are also some new experimental observations that cannot be explained by the classical Quark model, and the multi-quark component caused by the unquenching dynamics must be considered. Therefore, in order to truly understand the hadron spectrum and hadron structure, it is necessary to study multi-quark exotic hadron states.