Abstract: To improve the measuring accuracy and increase the signal-to-noise ratio(SNR)in ultrasonic detection of concrete damage,a frequency-modulated(FM)ultrasound transmission method was firstly developed.This method,due to transmitting an enveloped linear FM ultrasonic pulse,could enhance the emission energy without increasing the emission ultrasound pressure,and thus enhanced the effective disLance,measuring accuracy and signal-to-noise ratio.Then,the principles of pulse compression and decompression were discussed,and the electric circuit of pulse compression was devised.Experimental resuits show that pulse compression can improve measuring accuracy without reducing the effective distance.It can discover the flaws that can't be discovered by conventional detection methods.