The research work, Ascertaining the connection type between evaporating tube bundle and a steam drum shell on a Natural Circulation marine supercharged boiler, is important. For this reason the method, calculating the low-cyle fatigue life of supercharged boiler steam drums put forward by Xin-wei Zheng, et al., was put to use; Based on the relevant basic data from design department and two typical running conditions of one supercharged boiler, the cumulative fatigue damage ratio of welding technique was calculated. The calculated result proves that it exceeds the maximum value of 1.0 and the upper limit value of 0.75 in fossil-fuel power plants, respectively. So welding technique can’t guarantee the low-cycle fatigue life of this steam drum, the only connection type is expanded joint, and the connection type has been put into practice.