In the system, according to the offset switch, Golay complementary sequences Ak and Bk with the required length are decomposed into four unipolar electrical pulse signals. The four teams of electrical impulse signal are launched successively to drive the EOM to produce optical signals, and then the light pulse signal is coupled into the sensing fiber. Through the down-conversion subsystem, the Brillouin scattering signal is shifted to a low frequency band. After the A/D sampling a signal correlation processing is implemented and accordingly a Brillouin signal with higher SNR is obtained.