In a combustible energy recycling system and its method, the system includes an airtight incinerator body, a gas intake module and a blower. The incinerator body is filled with a combustible waste material, and the gas intake module installed in the incinerator body includes gas intake pipes, and one of the gas intake pipes is an ignition pipe for igniting the waste material in the incinerator body for a smoldering combustion, and an air outlet pipe of the blower is interconnected to the gas intake module for guiding outside air into the incinerator body, such that the outside air can move slowly upward with a high-temperature dense smoke produced in the smoldering combustion and surround every cross-section in the incinerator body for a uniform smoldering combustion, and a gas containing combustible energy in the dense smoke can be guided to a gas recycling mechanism for recycling and reusing the gas.