Study on quantity discount have been in two directions since Buchanen published that suppliers provide quantity discount for price discrimination and for channel efficiency. The model on quantity discount for price discrimination has been researched in economics. On the contrary, the model on quantity discount for channel efficiency has been sutdied in production management with assumptions and focuses different from economics. In this paper, the differents in two areas are analyzed and a two-stage quantity discount model is suggested. This model integrates quantity discount models researched in each area. In addition, the discount rate required in each stage for implementation of this model is suggested in both supplier side and buyer side under some conditions.