Abstract: The problem of guaranteeing real-time message transmission in LTPB network, linear token passing bus, has been studied. Bandwidth allocation for LTPB aims at real-time message transmission, and the key parameter, the minimum amount of time used for real-time message transmission in unit time, is an important factor to the property and validity of the bandwidth allocation. Having found out a defect in current real-time performance analysis method, we propose a concept of "the worst case situation", develop a reasonable model, get an important result in real-time performance analysis for LTPB network, and establish the analytic foundation to seek the better bandwidth allocation scheme.