Aimed at the early failure of the hub bearing of a heavy truck,a sealing unit with a rigidflexible combined sealing groove was designed.The finite element model of the sealing unit was established by the semisimplified finite element method,and the effects of the compression ratio of the sealing ring,the material hardness and the size of the sealing groove on the contact stress and the equivalent stress were studied.The interface program of the finite element analysis was compiled by using the VB language,and the key factors were optimized by taking the contact stress and the equivalent stress as the evaluation indexes of the sealing performance.The results show that the maximum contact stress and equivalent stress are increased with the increase of compression ratio and material hardness.With the increase of sealing groove size,the equivalent stress is decreased,while the maximum contact stress is first decreased and then increased.The compression ratio of the O-ring has the greatest influence on the sealing performance,following by material hardness and sealing groove size.The recommended values of the key design parameters are given:the initial compression ratio is 15% to 20%,the hardness of O-ring is Shore A 75 to 80,and the size of the sealing groove is 1.6 mm to 1.7 mm.The sealing effect of the designed sealing unit is verified by test.