Stainless steel 06Cr18Ni11Ti and cast steel 20Mn explosive welding composite plates can be used to build bridges in high alpine areas. Two groups of different welding parameters were used to investigate the weld interface characteristics of stainless steel 06Cr18Ni11Ti and cast steel 20Mn. The explosive thickness was 30 mm, the detonation velocity was 2300 m/s, and the stand-off distances were 4 mm and 10 mm, respectively. The morphology of the weld interface was studied using an optical microscope and scanning electron microscope, and the samples were submitted to tensile and flexural testing and hardness tests. Furthermore, the fracture morphology of the weld material was studied using a scanning electron microscope. In the interfacial morphology examination, the sample with a 10 mm stand-off distance had a thicker melting layer than the sample with a 4 mm stand-off distance. The melting layer thickens as the contact corrugation increases. Corrosion was observed on the cast steel 20Mn side of the weld interface enriched with austenite. The 4 mm stand-off samples did not exhibit apparent twins, whereas the 10 mm ones did. The 10 mm stand-off samples had higher interfacial deposition energy and strain rate, making twins more likely to occur. Tensile test findings indicated that all fracture separations occurred on the cast steel's 20Mn side. The shear strength of sample 1 ranged from 383.6 to 394.1 MPa, while that of sample 2 ranged from 394.3 to 408.4 MPa, showing binding strength across the interface greater than that of 20Mn. Both 10mm and 4 mm stand-off samples exhibited ductile fracture. In the 90 bending test, the welded interface shows no delamination or cracks, indicating outstanding bending performance. The hardness test results indicate that the hardness of cast steel 20Mn and stainless steel 06Cr18Ni11Ti after explosive welding are higher than that of the corresponding raw materials. Approaching the weld interface, the hardness increases noticeably. The maximum hardness for samples with a 4 mm stand-off is 413.2 HV, while for samples with a 10 mm stand-off, it is 407.9 HV. Work hardening is more pronounced on the 20Mn side of the sample with a 10 mm stand-off. The effect of hardening is much more noticeable. The fractures of the samples with 4 mm and 10 mm stand-offs display a river-like form in the fracture morphology study.