The invention relates to a method for reducing the internal temperature of an airtight device. The upper cover plate of a case is designed into upper and lower two layers under the premise of guaranteeing the IP protection grade, EMC and stable and reliable work of the device; a concave water guide groove and a hidden breathing and radiating hole are formed in the lower layer, a metal dust screen is arranged under the hidden breathing and radiating hole, and a heat transfer plate and a cooling fin are additionally arranged at the bottom and the top of each element high in power and prone to generate heat, and then, the temperature in the airtight device can be reduced; meanwhile, a CPU working plug-in is provided with a temperature and humidity chip for acquiring the temperature and the humidity inside the device in real time. According to the method for reducing the internal temperature of the airtight device, the problem that a traditional case sealing cover plate fails in natural heat dissipation through convection is solved, and heat generated by the heat transfer types such as thermal conduction, convective heat exchange and radiating heat exchange inside the case is effectively reduced.