The invention provides a projector shutdown cooling method and a projector shutdown cooling device. The method comprises the following steps: after receiving a projector shutdown instruction, acquiring a preset number of power-off time continuously stored recently; matching the preset number of power-off time with preset time span ranges and acquiring multiple time span ranges which are successfully matched; judging whether continuous and identical time span ranges exist among the multiple successfully-matched time span ranges, if yes, selecting a cooling mode corresponding to the continuous and identical time span ranges according to a preset cooling mode and time span range mapping relation so as to perform shutdown cooling treatment on a projector, if not, acquiring the occurrence frequency of each successfully-matched time span range, and selecting a cooling mode corresponding to the time span range with highest occurrence frequency according to the preset cooling mode and time span range mapping relation so as to perform cooling treatment on the projector. The method and the system can be used for prolonging the service life of the projector.