The degradation of combined rotor ,the core parts of the gas turbine ,decreases the per‐formance of gas turbine in a large extent .In view of this ,it is particularly important to research the performance degradation of the combined rotor .The performance degradation characteristics of combined rotor were discussed ,from the perspective view of performance degradation caused by rod crack .The finite element model of the combined rotor was established .The crack exten‐sion rate of the rod was gotten by using the finite element model .Then ,the measurement of per‐formance degradation which was caused by micro cracks was put forward ,and the assessment of performance degradation was completed as well .The results showed that the micro crack exten‐sion rate got faster when the size of crack increased ;the microcrack tie rod with different distri‐bution form did make a difference to the degradation of the combined rotor as the adjacent microc‐rack tie rods led to the fastest degradation rate and the 180° distributed microcrack tie rods led to the slowest degradation rate .%燃气轮机的性能下降很大程度上是由于燃机的核心部件———组合转子的退化导致的，因此，非常有必要重点研究组合转子的性能退化规律。组合转子局部结构的损伤，必将导致整体性能的下降。从该角度出发，建立组合转子的有限元模型，对组合转子拉杆裂纹进行扩展计算，定义组合转子性能退化量，分析了不同尺寸的拉杆裂纹对转子性能退化的影响。研究结果表明：随着裂纹尺寸的逐渐增加，组合转子的退化速率逐渐加快；不同微裂纹拉杆的分布形式对组合转子退化程度影响不同，当微裂纹拉杆相邻分布时组合转子退化速率最快，裂纹拉杆180°分布时组合转子退化速率最慢。
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