In the traditional and static studies, the uncertainty caused by mergers mainly means that the participating enterprises have the information about their own production efficiency, while the external enterprises cannot recognize whether mergers will affect the efficiency of the participating enterprises. As a dynamic extension based on the traditional studies, this paper aims to explore the merger motivations, as well as the actual profit of the merged enterprises within the framework of sequential decision-making, assuming that there are leaders and followers in the market. According to the different roles of the merged enterprises, this paper compares four scenarios of mergers, demonstrating that mergers are profitable with the redistribution of the enterprises' roles, even the efficiency is reduced. Furthermore, from the viewpoint of merger-control policies, this paper theoretically discusses the timing of policy intervention and the auditing criteria of government mergercontrol. It is shown that when the government adopts“ex-ante intervention”, the consumer welfare standard is more precise and rigorous; by contrast, when the government chooses “ex post enforcement”, the social welfare standard has more advantages.