The invention discloses a method for manufacturing a terahertz quantum cascade laser (QCL) metal waveguide structure and a laser. The method comprises the following steps of: successively growing an etching stop layer, a lower contact layer, a multi-quantum well active region, an upper contact layer, an n-type heavily doped layer, and a low-temperature growth passivation layer on a semi-insulating GaAs substrate by using molecular beam epitaxy; forming non-alloy ohmic contact; successively depositing an electrical contact enhancing metal layer, a metal In layer and a metal Au layer on a receiver substrate; performing flip-chip bonding on a device substrate and the receiver substrate, depositing a SiO2 protective layer, applying photoresist, and baking the photoresist; stripping off the photoresist; removing the SiO2 protective layer; forming a Schottky diode to contact a upper electrode metal layer; forming a lower electrode metal layer; performing flip-chip bonding substrate cleavage and packaging. The method reduces contact resistance, avoids the large free carrier leakage of a terahertz photoelectric device caused by the diffusion of the uncontrolled doping distribution, and reduces a waveguide loss caused by a annealing process.