Purpose: Research on job crafting has thus far focused on how alter job demand and resources behaviors relate to employee task performance. However, job crafting behaviors do not necessarily have an impact only on task performance, but also on employees' contextual performance, a phenomenon that has little research in job crafting research. Therefore, this study aims to investigate the effect of job crafting on task performance or contextual performance and the mediating effect of work engagement between them in the Chinese context. Research design, data and methodology: In order to achieve the above research goals and test the proposed hypotheses, we used a cross-sectional design and a self-administered questionnaire to collect quantitative data from September 8, 2021 to September 27, 2021 among knowledge workers in Shandong Province various financial companies and finally analyzed 211 questionnaires. Descriptive statistics and research model analysis were performed using SPSS 25.0 Version and AMOS 27.0 Version to test the developed hypotheses. Results: The results are as follows; firstly, the study showed that job crafting of employees had a significant positive impact on task performance and contextual performance. Secondly, the higher job crafting of employees, the higher their work engagement. Thirdly, this study showed that work engagement of employees had a positive impact on task performance and contextual performance. Fourthly, we predicted and found that work engagement of employees had a positive mediating effect between job crafting and task performance and a positive mediating effect between job crafting and contextual performance. Overall, this study showed that the proactive job crafting behaviors of employees enhance their engagement for their work, which in turn improves task performance and contextual performance. Conclusions: This paper develops job crafting research by exploring the positive impact of job crafting on employees' task performance or contextual performance through their work engagement. It also proposes that both job crafting behaviors and work engagement are important approaches to improve employees' task performance or contextual performance. Practical implications for organizations, such as increasing employee' work engagement, as well as the limitations and suggestions are concluded for the future research directions.