The invention discloses a BLDC (brushless direct current) motor fault diagnosis system which comprises an MCU and a fault diagnosis protection module, wherein the MCU can be used for diagnosing a BLDC motor fault type by combining interrupt response and periodic duty with a BLDC motor fault flag bit state emitted by the fault diagnosis protection module, can be used for receiving a three-phase short-circuit state of the BLD motor, and can be used for realizing fault recovery on the BLDC motor trough a BLDC motor fault recovery flag bit and on-off of BLDC motor driving; the fault diagnosis protection module is used for performing current sampling on the BLDC motor, and can be used for triggering the fault flag bit according to current sampling of the BLDC motor and the three-phase short-circuit state of the BLDC motor; and a BLDC motor current limit value set by the fault diagnosis protection module is greater than an earthing short circuit protective threshold value. The BLDC motor fault diagnosis system can avoid failure in report of BLDC motor faults, and can realize BLDC motor fault recovery during driving cycle at that time.