Cross-border operation is the emerging operation mode of platform enterprises in recent years. Answering the question of whether the cross-border behavior of the head platforms will produce more extensive monopoly power is an important premise for building a platform economic governance system that can stimulate vitality, ensure security and give full play to the role of platform economy in empowering the high-quality development of regional economy. First of all, this paper combs the stylized facts of platform cross-border operation, and analyzes the two opposite mechanisms of platform enterprises' market power change during cross-border operation: leverage effect and competition effect. Secondly, using the new empirical industrial organization theory and making adaptive improvements according to the economic characteristics of the platform, the market power measurement model of platform enterprises is constructed considering network externalities and innovation factors. By adding a parameter reflecting cross-border behavior—business diversification degree—into the model, the actual value of market power under the two scenarios of single-field operation and cross-border operation can be measured, and the change of market power can be obtained by comparing the measurement results of the two scenarios. Empirical results show that: When considering the cross-border areas similar to the main business, the market power is unchanged or slightly decreased, indicating that the giant enterprises can maintain the original market power when entering the fields related to the main business, and there is a certain degree of leverage transmission effect. Meanwhile, when considering cross-border activities in areas that are quite different from the main business, the market power shows a declining trend, indicating that large cross-border behaviors can strengthen the degree of business overlap between large platform enterprises, strengthen market competition, and play a certain role in balancing the multi-market transmission of market power of large platform enterprises. On this basis, this paper puts forward a new judgment on the platform competition pattern: The market power of the leading enterprises in the platform market can be transmitted in a limited scope, but with the expansion of the business scope of the enterprises, the outcome of winner-takes-all is replaced by a new round of competition between large platform enterprises, and the platform competition changes from winner-takes-all to winner competition. Considering dynamically in the time dimension, the outcome of platform competition has changed from oligopoly to anti-oligopoly, and oligopoly enterprises are still facing fierce competition in the whole business field. This conclusion shows that in the scenario of cross-border competition, platform economy will play two roles in the high-quality development of regional economy: First, competition can better play the matching role of platform economy, promote the growth of economic aggregate, and create the material foundation of high-quality development of regional economy; Second, cross-border scenarios continue to stimulate new business models, helping regions find new growth points according to local conditions and narrow intra-regional gap. Finally, this paper gives corresponding countermeasures and suggestions: With service quality as the breakthrough point, platform enterprises are guided to exert the new infrastructure attributes in regional coordinated development; Enhance the correlation between platform business and regional characteristics, and shape unique growth points of regional economy.