The Symposium on Accelerator Physics originated from 1980’s, the beginning of the development of high energy accelerator in China. During the past three decades, this series symposium are supported not only by the labs and universities of China, but gradually attracts some national labs of USA. It covers nearly all the research fields of accelerator physics, from theory to machine performance, from simulation to data analysis, from small size industrial machine to huge high energy collider, from ring-based synchrotron light source, to future hard X-ray FEL, etc. As a tri-annually meeting, the 12th Symposium on Accelerator Physics, organized by the Particle Accelerator Branch of Chinese Physical Society, will be held in Lanzhou, Gansu Province of China, from Aug. 13-15, 2014. This 3-day symposium will be sponsored by the Engineering Physics Department of Tsinghua University, the Institute of High Energy Physics, and also locally supported by the Yuzhong Branch of Lanzhou University.