In the era of knowledge economy, knowledge based employees have irreplaceable importance to the sustainable development of enterprises. However, the various deviations in the performance appraisal of knowledge based employees, such as excessively quantified performance indicators, unreasonable assessment cycle, excessive evaluation standards etc., have led to the increasingly serious overwork problem of knowledge based employees. According to the goal orientation of performance appraisal, it can be divided into evaluative performance appraisal and developmental performance appraisal. Forced spontaneous overwork and spontaneous overwork are two forms of overwork of knowledge based employees. Different goal orientation of performance appraisal has different influences on overwork of knowledge based employees. This paper analyzes the overwork problem caused by the goal orientation of performance appraisal, and discusses how the performance appraisal of different goal orientations affects the overwork of knowledge based employees. Based on the self determination theory, motivation can be divided into autonomous motivation and controlled motivation. The perception of the external environment and the inner self of knowledge based employees affect individual motivation. It is concluded that the evaluative performance appraisal linked the appraisal results with salary, job promotion, etc., forms the high pressure, threatening atmosphere and enhances the individuals controlled motives, in order to complete the task and avoid punishment, resulting knowledge based employees in forced spontaneous overwork. Developmental performance appraisal links the assessment results with training development and career, etc., forms the incentive, self independent and inclusive atmosphere and enhances the individuals autonomous motivation, in order to pursue self achievement, resulting knowledge based employees in spontaneous overwork. Niu Jingrui | Li Guangyi "Research on the Impact Mechanism of the Evaluative and Developmental Performance Appraisal on Overwork of Knowledge-Based Employees" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-3 | Issue-6 , October 2019, URL: https://www.ijtsrd.com/papers/ijtsrd29202.pdf