By packaging different kinds of products, firms always use mixed bundling to gain competitive advantages. In traditional markets, single-product firms mainly bundle products through merging its complementary firms. As antitrust authorities pay more attention to mergers, some firms are turning to engage in mixed bundling by contracts. For example, mobile phone firms and telecom service providers offer contract plans and prepaid plans with mobile phone, which are essentially mixed bundling. With the development of information technology, more and more internet enterprises have begun to implement the“mixed bundling contracts”. In this context, the“Anti-Monopoly Guide on Platform Economy”issued by the State Council of China has made it clear that platforms may adopt bundling and restrict market competition, which has been emphasized as“enhancing antitrust and prevent capital sprawl”in the 14th-Five-Year Plan of China. Thus, it is of great significance to analyze the motivation of manufacturers to implement mixed bundling contracts and its influence on the market competition for a better business environment and the improvement of anti-monopoly policy.

Based on the research of Choi（2008）and Armstrong and Vickers（2010）, this paper constructs a dynamic game model to study the competition problem of oligarchic firms that produce complete complementary products by signing the“mixed bundling contracts”strategy, which is common in the real telecom market, computer hardware and software market and other service markets. The results show that: In the case of one-sided bundling contracts, contract firms will gain competitive advantages by increasing the bundling price and reducing the component price through mixed bundling contracts, while its competitors are forced to lower their prices and fallen into a competitive disadvantage. In the case of two-sided bundling contracts, firms’ profit decreases though the bundling price decreases and the component price increases, but consumer surplus still increases and the total social welfare decreases. Finally, all of the firms choose to sign contracts with mixed bundling and fall into the“Prisoners’ Dilemma”. Thus, competition policy should be opposed to the strategic behavior of firms negotiating and signing contracts with mixed bundling.

The innovation of this paper lies in that: It develops a unified analytical framework based on Choi（2008）and Armstrong and Vickers（2010）, which extends and deepens existing studies. In particular, due to the interactive influence of the“vertical externality”of complementary products and the“horizontal externality”of competition, the results are different with previous studies. It also explains the competitive strategy of firms and the mechanism of bundling through mixed bundling contracts, providing a new perspective for understanding the bundling motivation. The research of this paper has important application value in reality. For example, in the telecom market, we observe that some telecom operators negotiate with mobile phone firms to sign contracts with mixed bundling to compete with their rivals. Based on the conclusion of this paper and the implementation status of anti-monopoly policy in China, policy suggestions are summarized as follows: （1）When antitrust authorities evaluate the effect of bundling competition, the product characteristics and market competition status should be considered.（2）Antitrust authorities should understand the motivation of bundling and evaluate the long-term welfare effect of mixed bundling contracts.（3）It is suggested to introduce third-party evaluation to build a multi-level governance model of mixed bundling contracts.