The invention relates to a cool / hot double-pipeline visible safety device for a biological fermentation tank, belonging to the technical field of beer fermentation equipment. The technical scheme is as follows: the cool / hot double-pipeline visible safety device comprises a pressure meter, a hot water pipeline valve A, a cooling medium pipeline valve A, a sight glass sheet A, a sight glass A, a filter screen A, a silica gel sealing gasket A, a movable joint A, a movable joint B, a safety valve, a movable joint C, a movable joint D, a hot water pipeline valve B, a cooling medium pipeline valve B, a sight glass sheet B, a sight glass B, a filter screen B, a silica gel sealing gasket B, a fermentation tank jacket and a temperature indicating meter. In order to heat or cool the fermentation tank, the cooling medium or hot water pipeline valve is closed, and the hot water or cooling medium pipeline valve is opened; and the hot water or cooling medium heats or cools the fermentation tank through the hot water or cooling medium pipeline valve, sight glass and fermentation tank jacket. In the heating or cooling process, the flow state of the hot water or cooling medium can be observed through the sight glass, the pressure meter displays the pressure of the pipelines and jacket, and the pressure can be automatically relieved under the condition of overpressure, thereby ensuring the safe and controllable production process.