The important purpose of performance appraisal is to encourage employees to make performance progress. This paper analyzes the relationships among guanxi practices within organization, measurability of appraisal criteria, appraisal fairness, and the employees’ motivation to improve performance in the context of Chinese “guanxi” culture. Based on 511 data of questionnaire，the results show that employees’ perception of guanxi practices has the negative effects on the employees’ motivation to improve performance, and appraisal fairness acts as a complete mediator between guanxi practices and motivation to improve. The measurability of appraisal criteria has positive effects on the employees’ motivation to improve performance, and appraisal fairness acts as a partial mediator between measurability of appraisal criteria and employees’ motivation to improve performance. Guanxi practices and measurability of appraisal criteria has interactive effect on employees’ motivation to improve performance, and guanxi practices negatively moderates the relationship between measurability of appraisal criteria and employees’ motivation to improve performance.