A variable speed fan motor, including a variable speed motor body and a motor controller. The motor controller includes a microprocessor, an inverter circuit, a gear detection circuit, and a power supply. The gear detection circuit includes a plurality of current sensing units. Only one of the power input lines is in an energized state, and remaining power input lines are in a deenergized state. Each power input line is connected to one current sensing unit. An output end of the current sensing unit is connected to an input end of the microprocessor. The microprocessor selects operating parameters of the motor according to a detected signal of energization state of each power input line. The microprocessor is connected to the series communication unit. The microprocessor communicates with an external device via the series communication unit.