Abstract: ［Objective］ During the propagation of guided waves in rails, there are problems of poor anti-interference ability and severe signal attenuation, which hinder the identification of rail bottom cracks. To improve the signal-to-noise ratio, it is necessary to propose a signal enhancement technology to strengthen the guided wave signal. ［Method］ Based on the traditional ultrasonic guided wave detection, Barker code is used as the pseudo-random sequence code, and BPSK (binary phase shift keying) technology is adopted to obtain a new excitation signal after coding and modulating the original excitation signal, achieving the spread spectrum processing of the excitation signal, to despread the collected received signal. An ultrasonic guided wave rail bottom crack detection test platform is built, and comparative tests are conducted on artificial cracks of different sizes at the rail bottom. The attenuation coefficients of the received guided wave signals are calculated respectively under spread spectrum and non-spread spectrum conditions of the excitation signal. ［Result & Conclusion］ The experiments prove that after the guided wave signal is processed by the signal enhancement technology, the attenuation coefficient is significantly reduced when propagating the same distance compared with the original unprocessed guided wave signal, and the ultrasonic guided wave signal is able to travel a longer distance. The effect is more obvious for artificial cracks of the same size, and the detection sensitivity of ultrasonic guided waves for rail bottom cracks is significantly improved.