In order to solve the problem of low accuracy caused by the delay of Beidou single point speed measurement of corn topdressing machine, a double speed measurement mode combining Beidou single point speed measurement with ground wheel speed measurement was proposed. The control system of corn topdressing machine was set up and the corresponding control interface was developed. The double speed measurement mode rule was established and the controller program was designed. The speed range of acceleration and deceleration process judgment and stable speed measurement of ground wheel were studied. The switching conditions of dual speed measurement mode were determined by experiment, and the feasibility of dual speed measurement mode was verified. The test results showed that the maximum speed of the ground wheel was 6.0km/h, the optimal value of the ground wheel speed measurement queue N was 5, and the critical value of mode switching speed variation coefficient was 4.2%. The speed measurement performance comparison test results of four different target speeds of 3.5km/h, 5.5km/h, 6.0km/h and 8.0km/h showed that the average response time of double speed measurement mode was 1.6s earlier than that of Beidou single point speed measurement, and the deceleration phase was 1.8s earlier. The actual fertilization distance was reduced by 0.55m. The results of field fertilization performance test showed that the average speed difference of fertilizer application was 1.5r/min in the acceleration stage of double speed measurement mode, and the maximum speed difference was 7.1r/min at the speed of 8.0km/h in deceleration stage. The results showed that the average response time of the system was 1.3s, the average steady-state error was 0.8r/min and the average overshoot was 8.7%. The accuracy of double speed mode switching was 100%, which met the needs of precision fertilization.