On Dec.12, 2005, the BESIII (Beijing Spectrometer III) mechanical system passed the acceptance test supervised by an experts' group. Hesheng Chen, Director of IHEP and Qinxin Ren, General Manager of Citic Heavy Machinery Co.Ltd. were present at the appraisal.

　　The system was designed by the Center for Experimental Physics of IHEP, contracted to and fabricated by the Citic Heavy Machinery Co. Ltd through strict public bidding process. All the components of the system were tested, assembled and commissioned at Citic. The installation started in July and was successfully completed at the end of November, 2005.

　　The newly –built mechanical structure of BESIII, 11 meters long, 6 meters wide, 6.5 meters high with a weight of 650 tons, is composed of the base, barrel yoke, end yoke and its moving structure, positioning and supporting structure for BESIII sub-detectors. The system, being the base and main structure of BESIII and at the same time being the absorber of the muon detector, provides magnetic flux return for super-conducting magnets of 10,000 Gauss and constitutes the supporting structure for positioning, connecting, adjusting and fixing of the sub-detectors. Positioning precision and stability of the system will be the basis for stable operation of the BESIII sub-detectors.

　　After a careful and thorough test, the experts' group concluded: All the technical specifications meets the design requirements, the general performance and the main technical specifications arrive at the advanced level of similar equipments in the world. The successful acceptance test marks an important milestone of BESIII construction.