This paper is concerned with the performance assessment problem for linear time-variant (LTV) processes. It is a continuation of the work by Huang (J. Process Control 2002, 12, 707-719) with further theoretical development and industrial applications. Systematic algorithms and procedures for the performance assessment of LTV feedback control loops are proposed. The developed algorithms are illustrated through a simulated stirred-tank heater example and, as an industrial case study, applied to a sulfur recovery unit that is under adaptive control.