Beijing Spectrometer III (BESIII) is a large-scale general-purpose magnetic spectrometer on the Beijing Electron-Positron Collider II (BEPCII). It has a total length of 11 meters, a width of 6.5 meters, a height of 9 meters, and a total weight of approximately 800 tons. Like the "eye" of BEPCII, BESIII is a combination of multiple particle detectors used to observe and measure various parameters of secondary particles produced by electron-positron collisions, such as energy, momentum, mass, position, and emission angle, so as to reconstruct the reaction process and study basic physical laws. BESIII is composed of a main drift chamber, time-of-flight counter, electromagnetic calorimeter, muon counter, superconducting magnet, and corresponding electronics, trigger, data acquisition and other systems. The electron and positron bunches in the double-ring collider collide at the center of the spectrometer, and all information about the generated secondary particles is recorded in real time by the spectrometer. After data processing, physical research in the tau-charm energy region is carried out.