This paper investigates the impact of product differentiation and competition on the airlines entry decisions into international air market where the nonstop and transfer product coexist. Using the liberalizing transatlantic market as an empirical study, this paper establishes a Probit model. The results show that: 1) The product differentiation degree significantly influences airlines entry decisions; 2) When the market share of an airline preexisting one-stop product is larger, the probability that the airline opens new nonstop intercontinental routes is larger; 3)In a liberalizing market environment, airline alliances are also one of the significant factors influencing airlines entry into the transatlantic market. The results can provide theoretical fundamentals and decision support for carriers to open new international routes.