Abstract: According to the arrangement of the anti-vibration bars (AVBs) and the number of continuous failure of in-plane supports, the in-plane constraint failure analysis of AVBs was classified into several cases. The effects of in-plane constraint failures on the in-plane modes of steam generator heat transfer tubes under different cases were analyzed. The mode damping ratio was calculated by performing a weighted average method based on the mode shape function, and then the effects of different constraints by AVBs on flow-elastic instability of steam generator heat transfer tubes were studied. The analysis results show that with the increase of the continuous failure position of the in-plane support, the first-order modal frequency in the elbow section area decreases continuously, and the more vibration modes appear in the elbow section. The first-order mode in the elbow section is not necessarily the mode in which the maximum flow-elastic instability ratio occurs. The vibration mode with the maximum flow-elastic instability ratio appears almost in the elbow section. With the increase of the continuous failure position of the in-plane support, the flow-elastic instability ratio increases continuously. When three or more in-plane constraints fail continuously, the flow-elastic instability will occur.