This paper studies the performance of trunk grouping in packet switch system design, with emphasis on the analysis of maximum throughput, input queue delay and packet loss rate. The trunk grouping technique can be implemented on both sides of the switch. In principle, the output trunk grouping relieves traffic output contentions, while the input trunk grouping, proposed in this paper, prevents individual input links from overloading. The study shows a significant advantage of both input and output trunk groupings in removing local congestions caused by individual links, especially in a highly nonuniform traffic environment. To implement trunk grouping, we suggest not to designate the connection of each virtual circuit to individual links in high speed network protocol design.