In order to ensure the structure safety of LNG heat exchanger in emergency stop operation process, the strength of brazed structure with rectangular fins and plates is investigated by means of finite element method. The microstructure of brazed joints and brazing filler is tested by metallographic examination with scanning electron microscope (SEM). The results show that the maximum shear stress is main reason to cause the structural failure in brazing seam while that at the brazed joint is mainly induced by the maximum normal stress. The peak value of Von Mises equivalent stress in brazed structure with rectangular fins and plates obviously and linearly increase with the HMR pressure when the temperature difference is less than 10K between HMR and LMR. At the same time, the peak value of Von Mises equivalent stress also increases with the equilibrium temperature and temperature difference between LMR and HMR. The aggregation of Si element in brazed joints and brazing beam will exacerbate the structural safety of brazed structure with rectangular fins and plates in the emergency stop operation process. The above results will provide some constructive guidance for the emergency stop operational process of LNG heat exchanger.