In order to solve the problem of poor vibrational localization of phase-sensitive optical time-domain reflectometer (Φ-OTDR) system caused by random coding method,a cascade modulation method of random code fused with long pulse is proposed.The acousto-optic modulator and semiconductor optical amplifier are used to realize the fusion modulation of random code and the long pulse,respectively,to improve the extinction ratio.The autocorrelation random code is used to generate the pulse train,and the digital quadrature demodulation algorithm is designed to obtain the beat frequency signal amplitude and phase information.The experimental results show that the scheme can improve the extinction ratio by 13.7dB with 40 ns-width pulse and 4 km-length sensing fiber.When the vibration signal frequency is 200Hz,the root-mean-square error of the vibration signal localization is 2.1m,and the maximal absolute error is 3.8m,which improves the vibration signal localization accuracy.The research provides a new method for the localization performance enhancement of the coded Φ-OTDR system.