Abstract: A new MAC protocol based on spatial TDMA for Ad Hoc networks using directional antenna was put forward.It adaptively chose interference angle threshold in terms of nodes position and antenna pattern,then applied greedy algorithm to generate pairs of nodes to realize high spatial reuse,and adopted piggyback technology to speed up information propagation all over network.The MAC protocol frame structure and corresponding algorithms were presented.Analysis and simulation results showed that our protocol can improve network efficiency,and was applicable for engineering fulfillment.