To highlight time-variant characteristics of indexes for bridge assessment process，a time-dependent variable weight approach is proposed． Initially，a typical variable weight model corresponding to the sum type balance function is established． In addition， index weights of suspension bridge superstructures are taken as an example to investigate the relationships between weights of replaceable/permanent members and operation time． Then，assessment results of the constant weight model，factor-based variable weight model，and time-＆ factor-based variable weight model for a suspension bridge are compared with each other． The results show that the assessment result of the time-＆ factor-based variable weight model mostly agrees with the actual condition of the studied bridge． It is concluded that index weights of replaceable members significantly gain in the end of their lives and have a periodicity with a period of the member service life; while，index weights of permanent members gradually increase over time． The time-dependent variable weight algorithm can adjust initial weights according to bridge operation time， which makes up the drawbacks of the factor-based variable weight model where satisfactory weight adjustment is unavailable on account of the low initial index weights．