The continuous development of digital markets has given rise to new business models and business behaviors, these models and behaviors have made digital market competition constantly dynamic and complex in its effects. The so-called dynamic feature means that the undertakings constantly adjust their business behaviors according to the changes in market supply and demand; while the so-called complexity of the effects shows that it is difficult to conclude the competitive damages and economic gains arising from the changes in these business behaviors and models. Therefore, it is often tough for China’s antitrust authorities and courts to evaluate and confirm the size and illegality of the competitive harm generated by these new business practices when applying the rule of reason. However, the less restrictive alternatives test, which was nurtured in the antitrust judicial process in the U.S., though had not been adopted by the U.S. Supreme Court prior to the American Express case, can be used as a key step of the rule of reason to streamline the complex economic efficiency analysis. This enables it to be applied in antitrust cases in digital market. The U.S. case law practice has established standards and procedures for the application of the less restrictive alternatives test, making it smoothly applied and thus supported by antitrust scholarship. Because of its ability to simplify the measurement of competitive gains and losses under the rule of reason, the test can achieve the dual goal of antitrust in digital markets, i.e., to maintain healthy market competition while maximizing the economic efficiencies of business conducts at the same time. Moreover, because the test is highly compatible with the dynamic and complex digital market competition, it can effectively reduce the ambiguity and arbitrariness of the rule of reason at the present stage in China. It can also improve the precision and efficiency of antitrust enforcement in the digital market. Nevertheless, the antitrust authorities and courts also need to take this test meticulously, as mistakes in the proposal of comparable alternatives could lead to false positive errors and in turn stifle sound business practices. From the perspective of legal principles, the test embodies the proportional quality inherent in the rule of reason; at the level of legal rules, the test could be systematically interpreted in the provisions involving the analysis of the theory of harm of cartels, abuse of dominant position and mergers; in terms of the specific implementation of the law, it is necessary to closely combine with the double-or multi-sided feature, diversified economic efficiency, and innovative and dynamic characteristics of the digital market when determining the effects of the behavior at issue. However, due to the shortcomings of the test and the difference of its meanings between the ancillary restraint doctrine and the general rule of reason, it is nonetheless necessary to untangle the levels and limits of its application.