Abstract: For momentum wheel product's development and lifetime assessment, the physical failure model test is conducted. Because the momentum wheel failure is represented as the failure of its bearing assembly lubrication system, the bearing assembly is selected as the test model. In this paper, we has analyzed the real working environment of momentum wheel bearing assembly, determined the ground simulation specification of the test model, then the effecting factors of bearing assembly lubrication system failure are analyzed, after that to determine the sampling scheme. Finally, the mathematical presentation of the failure of bearing assembly lubrication system is given. For the assurance of momentum wheel product lifetime assessment, it is believed to produce two important tribology matching tests during production is necessary.