Abstract: In this paper, a Lamb wave real-time monitoring system for monitoring curing process of epoxy resin at the medium temperature of 85℃ is proposed. The curing process of epoxy resin with different thickness in steel tank was monitored by both A₀ mode and S₀ mode of Lamb waves at the medium temperature of 85℃ and the change law of the attenuation coefficient of Lamb waves with curing time of epoxy resin was studied. The results show that acoustic attenuation coefficient of A₀ mode inepoxy resin in the curingprocess has poor consistency and instability, while acoustic attenuation coefficient of S₀ mode has good consistency and stability, which first decreases slightly, then increases rapidly, and then gradually decreases and tends to be stable. It can accurately characterize different curing stages of epoxy resin including the initial viscous flow, gel and glass stages. This study provides basic data and technical support for the design and optimization of resin matrix composite molding process based on Lamb wave on-line monitoring method.