High-density WiFi networks have been deployed in large-scale public areas to provide cost-effective Internet access for mobile end-users in recent years. While pedestrians are wandering around in WiFi coverage areas, the most essential issue is to establish and maintain connections between WiFi end-hosts and access points (AP) to deliver data effectively. As the resident time restricted by the end-user’s mobility and the limited WiFi coverage, the connection establishment and re-connection may significantly impact user’s experience and transmission efficiency of WiFi networks. We conducted a measurement study of dissecting WiFi connections on the real-world densely-deployed campus WiFi networks using an instrumented WiFi measurement framework. The whole connection setup procedure, consisting of Authentication-Association (AA), handshake and IP acquisition, is generally affected by AP densities, RSSI levels, pedestrians’ moving characteristics, etc. Mobile devices frequently attempt to establish wireless connections with available WiFi APs; nevertheless, the ratio of successful attempts is only about 10% in the observed measurements, which is quite low while pedestrians moving around in WiFi hot spots. Our field measurement may provide insights into designing the next generation software-defined WiFi networks for optimizing connection setup time, improving success connection ratio and achieving high effective data delivery.