With the development of e-commerce, the e-promotion and dualchannel supply chains has become a common phenomenon in society. And the promotional strategies of dual-channel supply chain members have become a popular studying topic. In this paper, a Nash equilibrium model is used to investigate the optimal promotion strategies of each member of the dual-channel supply chain when they are simultaneous and independent. By analysing the profit of joint promotions, it can be concluded that the profit is independent of both wholesale price and daily sales price. As commission increases, the profitability of the whole supply chain and of the platform provider increases, while the profitability of the supplier decreases. Therefore, in order to maximise the profits of each supply chain member, suppliers should strive for an equal share of the overall supply chain profits, while platform providers should refuse to share the overall profit of the supply chain equally with supply chain members.