The invention discloses a low-speed communication method applied to a control circuit board of a fan. The method comprises the following steps that the control circuit board is connected with a main controller; the main controller receives an analog signal of a speed-adjustment interface of the control circuit board, and through an analog-digital conversion module of the main controller, the received analog signal is converted into a digital signal; a judgement module is used for comparing the converted digital signal with V_THR, and when VSP is larger than V_THR, a logic high level is judged;when VSP is smaller than V_THR, a logic low level is judged; the main controller sends the type of a data package of an aging mode or a fault mode to the control circuit board through a protocol, thecontrol circuit board receives the data package and then explains data, according to the specific data, the aging mode is executed, a load is driven, or the fault mode is executed, fault informationis returned to, and accordingly low-speed communication between the main controller and the control circuit board is achieved.