Abstract: To resolve the problems of damage seed, complex machining and difficult exchange for traditional fixed board(belt) protecting seed device of metering device, the new protecting seed device was proposed. The structure and working principle were introduced, synchronization theory and maximum support force of protecting seed device was analyzed, critical condition of synchronizations was exported, and factors that impact on synchronization were obtained, maximum support force of protecting seed device was much smaller than seed compression failure force. The experiment results showed that the new protecting seed device decreased above 0.5% of rate of damage seed, and it was good at saving seeds and raised the germination rate of seeds.