The attenuation characteristics of Acoustic Emission(AE) signals in liquid and gas pipelines with complex structures are studied. By collecting acoustic emission signals of pipe body under different flow pressures, the amplitude attenuation law is analyzed, and the composition changes of pipe acoustic emission signals are studied by DB8 wavelet packet and Fast Fourier Transform(FFT). Through collecting acoustic emission signals before and after valve, flange, flow meter and other six kinds of pipeline accessories and analyzing attenuation law, it is found that electromagnetic flow meter is the pipeline component that has the greatest influence on the attenuation of acoustic emission signals. Then, the effect of fastening degree of bolt connection on signal amplitude and frequency components is analyzed. The results show that the higher the fastening degree of bolt, the lower the signal attenuation. The relevant research conclusions of this paper have integrated reference value and guiding significance for the sensor layout decision of acoustic emission detection of oil or gas pipelines in engineering.