Abstract: Limit device is an important control displacement structure of thermal power unit pipeline.At present,CAESAR Ⅱ software does not take into account the two different configurations of tie rod limit device and spherical disk limit device.Combining with the design of reheat section pipeline of a 660 MW power plant,the types of limit device,the processing method of CAESAR Ⅱ software and the arrangement of reheat section pipeline were introduced,the limit of tie rod was simulated,and a method of establishing the limit entity unit of tie rod in CAESAR Ⅱ software was proposed.The results of this method were compared with those of the conventional limit input method,and the influence of different input methods on the calculated value of pipeline thermal displacement was studied.The results show that when the thermal displacement of the hanging point of limit device was large,the tie rod limit device had a great influence on the thermal displacement of the pipeline.If the limit input mode of one-way displacement constraint was adopted with the conventional Restraints option,the deviation of the calculated value of thermal displacement would be large.CAESAR Ⅱ software could be used to establish the limit entity unit of the tie rod,so as to avoid the disadvantage of the actual thermal displacement of the pipeline to the selection of the support and suspension frame and even the safe operation of the pipeline due to the inconsistency between the actual thermal displacement of the pipeline and the design value.