Abstract: The response characteristics of the fuel rods in the sub-critical reactor of China Initiative Accelerator Driven System (CiADS) under beam trip were simulated by the reactor system analysis program RELAP5 mod4.0. The fatigue life of the fuel cladding in CiADS under beam trip is calculated by ANSYS 17.0. The fatigue life of the fuel cladding in hundred megawatt Accelerator Driven Sub-critical System (ADS) to be designed in China is predicted. The results show that the power of CiADS subcritical reactor instantaneously falls to 2.156% of full power when beam trip lost. The fatigue life of the fuel cladding of the CiADS subcritical reactor under beam trip is above 10⁸. the beam trip will not cause fatigue damage to fuel cladding in hundred megawatt ADS to be designed in China.