Abstract: A certain R60702/TA1/Q345R composite plate cracked near the base layer weld of the tube section, and the base layer of the base material composite plate had cracks. The reasons for the defects of the composite board base layer were analyzed by methods such as macroscopic inspection, chemical composition analysis, metallographic inspection and energy spectrum analysis. The results show that the defects of the composite board were a large number of non-metallic inclusions and precipitation phase bands in the base layer of Q345R steel, and cracks caused by non-metallic inclusions and precipitation phase.