The invention relates to a device for producing oil by carrying out pyrolysis on polystyrene foam plastics, belonging to the field of recycling of wastes. When the device is in use, the polystyrene foam plastics enters a screw extrusion device from a feeding port through a stock bin after being coarsely crushed, and heat is generated by means of extrusion and friction strain of a variable pitch screw, so that volume reduction of the polystyrene foam plastics is realized. An electromagnetic induction coil is wound on an external cavity of the outer wall of the device and can be used for enabling the variable pitch screw in the device to become an internal heat source for heating materials by means of self-heating. By adjusting the rotating speed of the screw, the polystyrene foam plastics can be enabled to maintain specific retention time in a specific area so as to be subjected to pyrolysis. Pyrolysis gas is discharged into a condenser pipe from a cavity under the condition of negative pressure and is then liquefied into oil, and exhaust gas of pyrolysis is absorbed by activated carbon, so that secondary pollution is reduced. The front end and the rear end of the device are respectively and externally connected with a vacuum pump, so that negative pressure and an oxygen-free environment are realized in a screw conveying device. The polystyrene foam plastics used by the device does not need to be cleaned, so that the production of cleaning waste water is effective reduced in a recycling process.