Abstract: Using the world′s largest sample of Ψ(2S) events collected at the Beijing Electron-Positron Collider, extensive studies on all 6 charmonium states below charm threshold have been conducted. Of more than 50 results including measurements of mass, width and branching fraction, 21 parameteers were measured for the first time, and a large part of the others were determined with the highest precision. A number of anomalies have been observed from a careful comparison of the branching fractions for various modes of exclusive hadronic decays of the J/Ψ and Ψ(2S), which pose a significant challenge to the present understanding of hadronic decays. This study is of importance to the test and development of quantum chromodynamics, and provides a solid foundation for continuing experimental studies of charmonium physics at an advanced level in China. It was awarded a 2nd Class National Science Award in 2001.