Abstract: The superconducting magnets are undeniably the core components of a tokamak device, playing a pivotal role in its operation. These magnets are subjected to extreme low-temperature environments and complex discharge scenarios during their service. To ensure the stable and reliable performance of these critical components under such harsh conditions, simulated tests are conducted within the Magnet Cold Test Bench （MCTB). Since the magnet support legs, as critical components for securing the magnets in MCTB, plays a vital role in structural safety, especially in the bolted connections, which are prone to failure and may lead to accidents, rigorous and comprehensive strength verification are required to ensure sufficient strength and stability in a 4 K service environment. In this study, the FIX_OIS support leg structure that bears a large load in MCTB is selected as the research object, and the steady-state thermal structure coupling analysis is carried out on it by using finite element software ANSYS. In view of the service conditions and fastening function characteristics of the support leg bolts in a low-temperature environment, the preload of the bolts has been adjusted and optimized, which not only reduces the risk of low-temperature brittle fracture of the bolts during operation, but also avoids the loosening of the bolts during the discharge process of the magnet. Then, the strength of the support leg bolts was evaluated by referring to the BPVC. VIII. 2—2021, JB 4732—1995 standard and VDI 2230—2015 standard. According to the evaluation results, the strength of the bolts all met the requirements of structural safety. This paper provides certain reference value for the analysis and research of bolt strength in ultra-low temperature environments such as fusion reactors.