Abstract: Q235 carbon steel/304 stainless steel composite plate was prepared by vacuum hot-rolled process with the first pass reduction rate of 30% and the second pass reduction rate of 0%， 10%， 20% and 25%， respectively. Then， the average grain size， dislocation density and residual stress of microstructures for substrate and composite plates were calculated， and the relationship among them was discussed. The results show that with the increasing of reduction rate， the area of interfacial ferrite region decreases gradually， and the geometric necessary dislocation density of substrate and composite plates at the interface shows an increasing trend. When the reduction rate of second pass increases from 0% to 20%， the average grain size of substrate carbon steel (GC) increases， and the dislocation density caused by plastic deformation of carbon steel increases from 0.49×1014 to 0.8×1014 m-2. The residual stress increases from 48.77 to 243.83 MPa. When the reduction rate increases to 25%， the GC size decreases， the dislocation density decreases to 0.67×1014 m-2， and the residual stress is reduced to 33.89 MPa. As the reduction rate increases， the average grain size of composite plate stainless steel (GS) increases continuously， the dislocation density increases from 0.58×1014 to 1.02×1014 m-2， and the residual stress increases from 45.93 to 91.86 MPa. The study results provide a theoretical reference for the rolling process and microstucture control technology of this type of composite plate.