The invention provides a spindle speed monitor for an omnidirectional submersible propeller. In the invention, an expected motor speed input by an upper computer is transmitted to the single-chip microprocessor of a main control unit through a serial port; the single-chip microprocessor converts the input motor speed into a control instruction based on a Modbus protocol which can be recognized by the frequency converter of a motor speed regulating unit, then adds a corresponding CRC check code and transmits the control instruction to the frequency converter through a MAX485 chip; meanwhile, the PTD7 pin of the single-chip microprocessor controls the MAX485 chip to work in a half-duplex mode for reading the motor speed and displaying the speed on the liquid crystal display (LCD) screen of an LCD unit in real time. The spindle speed monitor of the invention has the characteristics of high control accuracy, low operating voltage, low power consumption, good reliability, simple structure, long service life and the like. The spindle speed monitor can be matched with a submersible to monitor the spindle speed of the omnidirectional propeller at any time without professionals.