Based on the basic principle of magnetic flux leakage（MFL） detection technology, the finite element method and COMSOL software were used to simulate the magnetic flux leakage signals of crack group and pit group with composite defects of pipeline. The results show that for the crack group, with the increase of crack strips, the amplitude of radial component B,x, and axial component B,y, of the flux density increase significantly, and the space of peak valuesof B,x, shifts to both sides, and the width of B,y, waveform increases slightly. When the metal loss volume is the same, the peak values of the radial and axial components of the flux density are not only related to the defect size, but also related to the defect distribution. For the compound pits distributed along the axial and circumferential directions, when the pits are superposed with each other, the magnetic flux leakage signal changes in the overlapping part of the pits. When the pits are separated from each other, the magnetic flux leakage signals of the two pits are independent of each other, and the signal strength does not change significantly with the increase of the pit distance. This provides a theoretical basis and reference for the analysis of the leakage signal characteristics of the defect group.