<p>Control bus system (CBS) is critical communication infrastructures in flight vehicle control system, and their health condition directly affects signal transmission quality. Existing health assessment methods based on transformation matrix with precise quantitative value are commonly used to address the inconsistency between indicator reference grades and assessment grades. However, in practice, precise quantitative values are often difficult to obtain because expert knowledge is usually incomplete and uncertain, which reduces the credibility of the assessment results. To address this issue, this paper proposes a novel health assessment model based on the evidential reasoning rule with an interval transformation matrix (ER-ITM). First, an interval transformation matrix is introduced to characterize the uncertainty caused by data disturbance and errors in expert knowledge. Meanwhile, a new information transformation technique is developed to enable information conversion between different assessment frameworks. Second, based on parameter calculation, the iterative evidence combination process is transformed into an optimization problem with interval parameters, thereby establishing a complete health assessment model. Finally, sensitivity analysis is conducted to identify the most influential links in the proposed model. A case study of a control bus system is presented to verify the effectiveness of the proposed approach.</p>