The large furnace, which could withstand temperatures of more than 1,000C, was constructed weeks before the journalist's death, according to a new documentary.
It was at the home of the Saudi consul-general in Istanbul, just a few hundred yards from the consulate building where Khashoggi, 59, was killed in October last year.
Turkish authorities believe that after he was strangled to death, his body was dismembered with a bone saw and parts were taken to the address and burned.
A large amount of meat was burned in the oven afterwards to cover up what had happened, it is alleged.
The oven was seen burning in the aftermath of Khashoggi's disappearance, and Turkish authorities believe the body was destroyed over three days, an Al Jazeera investigation found.
A worker who helped build the oven said that the Saudi consul gave very specific instructions - saying it needed to be deep and capable of melting metal.
The claims were made in an Al Jazeera documentary screened on Sunday.
The programme also states that Turkish intelligence chief Hakan Fidan, who was investigating the journalist's disappearance, demanded that Saudi Crown Prince Mohammed bin Salman explained to him what happened.