The effects of change in microstructure and residual stress distribution on Barkhausen noise (BN) on the bainitic steel side in a welded bainitic and austenitic steel pipe are studied. Test results show that with the increase of distance from the weld fusion line the microstructure on the bainitic steel side could be divided into the following four regions. They were coarse lath bainite plus martensite region, uniform and fine granular bainite (normalized structure) region, coarser granular bainite plus a small amount of block-like ferrite region (transient region) and original granular bainite region. The residual stress along the longitudinal direction of the pipe after welding was gradually decreased with the increase of distance from the weld fusion line while the characteristic of the residual stress along the peripheral direction of the pipe was not obvious. The ringdown count rate of BN had the highest value near the fusion line and the lowest one at a 10mm distance from the fusion line on the bainitic side, then tended to increase gradually. The test results are analyzed and discussed in the paper.