After the COVID-19 pandemic has subsided, the catering industry has returned to its previous thriving scene. Many restaurants have launched group buying services and collaborate with third-party online platforms to attract more customers. For the optimal decisions and maximum profits of restaurants and online platforms, a two-layer supply chain model is designed to investigate and study the price strategies and service strategies. Considering the service levels of restaurants and platforms, we construct the mathematical expressions of the offline retail model, online retail model, and online group buying model, respectively, and solve the game equilibrium. The results are shown as follows: (1) With cooperation between the restaurant and platform, both the restaurant and platform can obtain their maximum profits when they apply optimal pricing strategies. (2) The optimal pricing strategies of the restaurant are influenced by the sensitivity coefficients of customers to the restaurant and platform’s service levels, and the cost coefficients of the restaurant and platform’s service levels. (3) The maximum profit of the restaurant is directly proportional to the number of new potential consumers who are attracted. The more potential consumers who are attracted, the higher the profit the restaurant earns. The research results provide a reference for restaurants and platforms to formulate price strategies and service strategies, to help restaurants and platforms achieve more profits.