Abstract: Electric Propulsion Plume Diagnostic System （EPPDS）is a self-developing equipment used for the space electric propulsion plume diagnostic, which consists of the probe assembly, moving platform and control unit. The reliability index for EPPDS was required that the MTBF （θ₀） must be greater than or equal to 5 000 h. According to the reliability prediction theory of MTBF with series-parallel system and the distribution of exponential life model, the prediction produce of MTBF for EPPDS was provided, and the prediction for modules was carried out, and the predicted MTBF of system was 1.059×10⁴ h. According to the short-term and high-risk time terminated testing program in GJB 889, reliability verification testing enduring 1833 hours for three EPPDS indicated that all the output voltage parameters of power processing unit conform to the qualification criteria, including bias and sweep voltage for Fraday probe, Langmiur probe and retarding potential analyzer. The method can be applied to the prediction and validation of MTBF for other electro- mechanical products.