Based on the perspective of social relations, this paper examined the predictive powers of leadership-member exchange on knowledge sharing, and the mediating role of workplace friendship between them. Furthermore, we also examined the moderating role of power distance between leadership-member exchange and workplace friendship. Questionnaire survey data were collected from 214 railway workers in China. In general, the results show that: (1) the leadership-member exchange has a significant positive impact on the knowledge sharing; (2) workplace friendship plays a partial mediating role between leadership-member exchange and knowledge sharing; (3) power distance plays moderating role between leadership-member exchange and workplace friendship. The higher the power distance perceived by employees, the weaker the positive relationship between the leadership-member exchange and the workplace friendship. Finally, theoretical and practical implications were put forwarded stemming from this study and the suggest directions for future researches were also provided. © 2018 IEEE.