Abstract: An ultrasonic test with RAM-5000 SNAP is performed in water to measure the transmission signals(including the fundamental and second harmonic)of epoxy bonded structure,the repeatability errors are below 1%and 3%,respectively.A back propagation neural network is used to predict the tensile strength with the surface roughness as well as amplitudes of the fundamental and second harmonic being input parameters;the arithmetical mean error is 8.3%.This provides a possible way to predict the tensile strength of bonding structure.