Signal enhancement of ultrasonic guided waves is studied using time reversal technique. The defect in pipe is detected by activating single mode guided waves L(0,2) at the center frequency of 70 kHz. Time-reversal technique is used to further enhance the defect detection capability. A method to identify the defect is described on a finite element model. Numerical results show that the time reversal technique has the ability to evidently enhance the amplitude of damage reflected wave and improve the detection efficiency of defect.