InfiniBand Architecture (IBA) is defined as a switch-based interconnection technology with high-bandwidth and low-latency. It is suitable for constructing high-speed networks for cluster systems and has been ratified as a new industry standard for the server I/O and inter-processor communication. In this paper, we propose an efficient flow control mechanism with job threshold for InfiniBand networks. This new scheme can reduce the delay, blocking probability, and mean queue length as well as enhance the Quality of Service (QoS) of InfiniBand networks. The principle of maximum entropy (ME) is adopted as an effective methodology to analyze the new mechanism with the generalized exponential (GE)-Type distribution for modeling the inter-arrival times and service times of the input traffic. Moreover, typical numerical experiments are included to validate the results of ME algorithm against simulation.