A method for updating a firmware of a complex programmable logic device comprises: electrically connecting a general purpose input/output pin of a baseboard management controller with a hitless enable pin of a complex programmable logic device; electrically connecting a first integrated circuit bus of the baseboard management controller with a second integrated circuit bus of the complex programmable logic device; inputting and transmitting a update command to the baseboard management controller by a local operating system; enabling the hitless enable pin by the baseboard management controller according to the update command; cleaning a first firmware in the complex programmable logic device by the baseboard management controller according to the update command; and burning a second firmware into the complex programmable logic device by the baseboard management controller according to the update command.