The crankshaft of a 6 crank reciprocating compressor frequently cracks and often scuffs because of torsional vibration. Such problems are solved by connecting the interference hot assembling two plate flanges. With the help of ANSYS software, finite the 1^st and 2^nd crank bearing 2^nd and 3^rd shaft by means of element analysis model is set up for pre-and-aft modification of crankshaft. Modal analysis and dynamic response calculation of crankshaft for different modification plans are performed, and the results show that the frequency ratio r between sevenfold rotating speed of initial crankshaft and the first order torsional vibration natural frequency is 1. 016, which makes the initial crankshaft resonates. With the rotating inertia-mass of modified crankshaft enlarged, to 1. 064, and resonance is eliminated. The rotating vibration displacement of initi the frequency ratio r increases al crankshaft at the first crank pin is far bigger than that of the 6^th, which is the main reason of crank bearing scuff. The inertia-mass of initial crankshaft results in additional stress at resonance, which is the main reason of crank cracking.%某6列氮氢往复压缩机因曲轴扭转共振，出现轴颈裂纹及第1、2列连杆瓦烧瓦现象，曲轴在2、3列间通过热装两个连接盘进行对接，问题得到解决。利用ANSYS分析软件，建立修改前后轴系有限元模型，分别对轴系进行模态和动态响应分析发现：修改前轴系7倍压缩机转速与1阶扭转固有频率比r为1．016，轴系出现共振，修改后轴系因增加旋转惯性质量r增到1．064，共振消失；修改前轴系第1列曲柄销扭转振幅远大于第6列，揭示了第1、2列连杆瓦烧瓦的原因，轴系共振时惯性载荷引起附加应力是曲轴出现裂纹的根源。
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