The invention discloses a device utilizing waste plastics to thermally convert and prepare hydrogen-rich syngas and a process. The device utilizing the waste plastics to thermally convert and prepare the hydrogen-rich syngas comprises a waste plastic horizontal pipe type furnace steam pyrolysis part, a high temperature water steam gasified part, a cyclone separation dust remover part and a high temperature melting part. The device utilizing the waste plastics to thermally convert and prepare the hydrogen-rich syngas and the process pyrolyze waste plastics firstly, and generate pyrolysis mixture gas and solid residue. The pyrolysis mixture gas intensifies water steam to gasify and convert to be hydrogen-rich syngas through adsorption of carbon dioxide (CO2), the solid residue is treated in a molten pool in high temperature of 1400-1600 DEG C, and combustible components are burnt out in high-temperature processing, and also play the role of thorough destroyed poisonous. Residue which is discharged from the molten pool is used as building materials at last, is safe to use, the whole processing process does not generate secondary pollution, and the device utilizing the waste plastics to thermally convert and prepare the hydrogen-rich syngas and the process are an extremely thoroughly environment-friendly energy conversion processing technology of waste plastics.