The Muon System is the first BESIII subsystem that has been installed. The installation had started from July this year. In order to speed up the installation, a crisscross working mode had been adopted, in which the installation team and the engineering team worked in turns. Only after numerous difficulties being overcome, had the installation been accomplished ahead of schedule.

　　The Muon System has adopted a new type of gas detector with RPC cells, which is now very popular in the world. Since the beginning of 2002, under undesirable conditions, the Muon Group had summed up lessons and experience drawn from both domestic and abroad. In less than three years, a high-performance RPC detector with our own intellectual property has been successfully developed.

　　On the afternoon of October 14th, a celebration ceremony was held on the BESIII site to hail the milestone, BESIII staff together with representatives from institutions taking part in the fabrication and installation attended the ceremony.