Acoustic emission (AE) test monitoring is an effective non-destructive technique. In the paper, a new damage assessing method which is damage acuteness index for AE signal of PZT patches based on fractal theory was proposed. The damage index was deduced by the character of signal analysed by fractal theory. It is deduced that both the curve length and the fractal dimension (FD) of signal are related with damage development. The AE test of Pseudo-static experiment of a concrete-filled GFRP tubes (CFFT) was performed for validation. The results show that the damage acuteness index can assess damage development process effectively. So the damage acuteness index is a promising method to apply in AE test monitoring.