In the "Internet +" environment, the fresh agricultural products online retailers (the FAPOR) face a dynamically changing market environment. How to form the dynamic marketing capability that effectively responds to market changes has become an important issue for the FAPOR to solve urgently. Taking the FAPOR "BenLaiShengHuo" as an example and collecting a lot of first-hand data and second-hand data, through the open coding, spindle coding and selective coding to analyze the case data, this paper explores the dynamic marketing capability formation process of the FAPOR. The elements of the dynamic marketing capability of the FAPOR and their functions are obtained:based on the capability of consumers connection to excavate the demand characteristics of the consumers, based on the capability of channels management to layout omni-channel consumption scenarios, based on the capability of producers management to continuously obtain high-quality agricultural products,and based on the capability of brand promotion to constantly optimize the corporate image. On this basis, the logic relationship between the various capabilities is analyzed, and the dynamic marketing capability formation mechanism of the FAPOR is obtained. That is, the capability of consumers connection promotes the formation of the capability of channels management and the capability of producers management, the capability of channels management and the capability of producers management accelerates the formation of the capability of brand promotion, the capability of brand promotion further strengthens the capability of consumers connection. The interaction of these four kinds of ability forms the circulation of closed-loop relations, continuously improves enterprise's dynamic marketing ability. Finally, some relevant management implications are put forward.