Consider a two-echelon supply chain with one supplier and two retailers. Optimal pricing and input decisions are discussed under yield uncertainty. Under a basic model, firstly, the supplier determines his optimal input quantity under yield uncertainty, and decides his optimal wholesale price when the actual output quantity is found. Then the retailers determine optimal order quantities. On this basis, the competition model considering a supply commitment is proposed. The competition equilibriums are discussed by using backward induction. Numerical analysis shows that the performance of the supply chain can be improved after introducing the supply commitment with certain parameter conditions.