The invention discloses an extra-cavity laser frequency conversion system and method, relates to a system and method for rapidly acquiring efficient extra-cavity laser frequency conversion, and belongs to the field of mutual action of lasers and substances. The system and method solve the problems that an existing extra-cavity laser frequency conversion method is poor in frequency multiplication efficiency, and an extra-cavity laser frequency conversion system is low in automation degree. A nonlinear crystal is placed on a crystal rack, laser beams are transmitted into the nonlinear crystal in an incident mode, wherein the laser beams are formed by lasers emitted by a short-pulse laser device after the transmission direction of the lasers is adjusted through a diaphragm, hybrid light after frequency conversion through the nonlinear crystal is transmitted into a filter in an incident mode, target laser beams after being filtered by the filter are emitted to a polarizing film or an attenuation piece, laser beams emitted through the polarizing film or the attenuation piece are transmitted to a light-sensing surface of a photoelectric detector in an incident mode, the light intensity electric signal output end of the photoelectric detector is connected with the light intensity electrical signal input end of a computer, and a serial port of the computer is connected with the displacement signal input end of a stepping motor through a data line. The extra-cavity laser frequency conversion system and method are suitable for extra-cavity laser frequency conversion.