Measuring the ground speed is important for a variable rate fertilizer machine. Since the working environment is hard, the reliability and anti-jamming capability of the ground speed collecting system is poor. A ground speed collecting system for a variable rate fertilizer machine is developed based on Bluetooth. The ground speed sensor of the system is a photoelectric encoder, which is set on one of the wheels of the machine. An ARM microprocessor is used to receive input signals from the ground speed sensor, and calculate the working speed. And then the working speed signals are transformed into the Bluetooth signal format, and transmitted to variable rate fertilizer controller by the KC111 adapters. The maximum error of the test is 2.92%. It shows that the developed system is practical. 