Abstract: Institute of Mechanics (IM), Chinese Academy of Sciences (CAS), originated from Mechanics Laboratory of Institute of Mathematics (of which CHIEN Wei-zang was the director), was founded under the help of Peking University and Tsinghua University. The founding background and process of IM were retrospected and illustrated, the acts of Tsien Hsue-shen during IM’s construction and his thoughts on the development of IM, as well as the development goals and visions proposed by some prominent persons when they were discussing the construction of IM on the executive meeting of CAS, were reviewed. Finally, the founding personnel constitution of IMCAS was introduced.