Titanium-steel composite plates with large sizes of 4260 mm×4260 mm×(6.5+32) mm were prepared by explosive welding technique. Ultrasonic nondestructive testing, phased-array waveform microscopy, optical microscope, and scanning electron microscope were used to analyze the mechanical properties and interface morphologies of the composite plates. Results show that when the detonation velocity, density, explosive height, and stand-off distance are 2200–2270 m/s, 0.80–0.82 g/cm³, 45.0–46.0 mm, and 8.0–11.0 mm, respectively, the mechanical properties of the prepared plates can satisfy ASTM B898-2020 technical requirements. The interface waveform presents a typical periodic combination morphology and the interface is clear and uniform. A small amount of solidified melt exists in the vortex area of waveform. The ratio of amplitude to wavelength ranges from 0.15 to 0.25, and the optimal shear strength can be achieved when the ratio is approximately 0.20. This research provides preparation technique for the large-size titanium-steel composite plates and theoretical guidance for the subsequent optimization of the explosive welding process of composite plants.