The invention provides a high-speed line patrol infrared optical system for an unmanned aerial vehicle. The system comprises an infrared thermal imager arranged on an optoelectronic pod of the unmanned aerial vehicle, wherein a lens switching device is arranged on an infrared light path of the infrared thermal imager and comprises a rotating shaft, a rotating angle sensor, a plurality of lens assemblies, a reducer, a servo motor, a wireless communication module, a pulse width modulation module and a single-chip; the plurality of lens assemblies are connected with the rotating shaft and arranged on the same straight line with a primary optical axis; the reducer is connected with the end of the rotating shaft; the servo motor is connected with the reducer and is used for driving the rotating shaft to rotate by driving the reducer; and the single-chip rotates the lens assemblies from an initial line position set by a lens initial line setting module to an operating line position set by a lens operating line setting module according to a rotating angle of the rotating shaft sensed by the rotating angle sensor by controlling the servo motor. Therefore, the primary optical axis of the lens assemblies is coincided with a center line of the infrared light path of the infrared thermal imager so as to enlarge a field of view of the infrared light path of the infrared thermal imager.