The invention discloses a cleaning method for a laser device cooling box and a detection method for detecting the cleanness of the cleaning method, and aims to provide a cleaning method which is convenient, precise, high in cleanness and capable of rapidly cleaning a cooling box of a complicated structure and a detection method which is simple, convenient, accurate and capable of quantificationally and precisely judging the washing cleanness. The cleaning method disclosed by the invention comprises the following steps: respectively connecting an inlet pipeline and an outlet pipeline of a water pump with a water inlet and a water outlet of a cooling water circulation loop of a cooling system of the laser device cooling box; filling pure glycol washing liquid into the laser device cooling box; subsequently putting the laser device cooling box full of the glycol washing liquid into an ultrasonic washer of which the temperature is regulated to 80 DEG C; starting the ultrasonic washer and the water pump to make sure that the glycol in the laser device cooling box can flow circularly under the effect of the water pump; performing a transmittance test on a standard glycol sample and a glycol liquid sample by using a spectrophotometer; afterwards comparing the transmittance test results of the standard glycol sample and the glycol liquid sample, wherein the cleanness is considered to be good if the sample transmittance is 2% smaller than the standard glycol transmittance.