Job knowledge characteristics have long been regarded as relatively fixed. However, this may no longer be the case given the dynamic and complex situations faced by employees during the COVID-19 pandemic. On the basis of event system theory and the work design literature, we argue that the onset of COVID-19 created an immediate decrease in job knowledge characteristics, which gradually increased over time in the post-onset period because of employees’ coping with the pandemic. The rate of increase in job knowledge characteristics is higher for those with higher individual task adaptivity than for others. We further argue that changes in job knowledge characteristics produced changes in job stress, and that this effect is weakened by job security. We conducted a 6-month, 6-wave longitudinal survey to gather data from 235 employees in Macau, China covering the pre-onset, onset, and post-onset periods of the COVID-19 outbreak. The results, based on discontinuous growth modeling and latent change score modeling, support our arguments. Our study advances the dynamic view of work design by identifying how a macro event may shape job knowledge characteristics and the implications of a time-to-time change in job knowledge characteristics. Overall, we suggest that there are psychological costs when employees cope at work with the business interruptions caused by COVID-19.