Abstract: Based on the transaction cost analysis of the enterprise vertical efficient boundary, the authors think that the thrift of transaction cost and the profit increase caused by the transaction structure are the driving force of enterprise vertical efficient boundary variance. Follow the method of O.E. Williamson, the authors use technical efficiency and agent efficiency to analyze the efficient boundary and discuss the hyper-competitive environment effecting on the efficient boundary. The conclusion is that the border will vary in certain ranges, so the transaction in the range can be governed by the inter-firm cooperation. And then, the authors propose a model of an enterprise vertical efficient border in the hyper-competitive environment.