Based on a supply chain consisting of two suppliers with different market sizes and an etailer, we studies sales format choice for the supplier with a larger market size considering both price competition and logistics service competition among products. The results show that the supplier with a larger market size should decide which sales format to choose according to the platform's logistics service advantage and the service competition intensity. Specifically, he tends to choose the agency selling(reselling) format when the platform's logistics service advantage is relatively low(high), and he tends to choose the reselling (agency selling) format when the service competition intensity is relatively low(high).