Welding defects can cause serious damage to the working operation of the steel welded structure. In order to study the influence of welding defects on the damage evolution of Q245R steel under bending load, bending experiments were carried out on Q245R steel specimens without defects and slag inclusion defects, and real-time monitoring was carried out using acoustic emission technology and digital image correlation methods. The results show that compared with the non-defect specimens, the characteristic parameters of the acoustic emission signal amplitude, the cumulative number of impacts and the energy of the slag inclusion specimens are greatly increased, and the amplitude and energy of the slag inclusion specimen are as high as 80.5 dB and 231.2 mV·ms, respectively. Under a load of 3.3 kN, the maximum displacement field of the slag inclusion specimen is increased by 21.093 mm. The experimental results can provide a reference for the health monitoring of steel welded structures.