Abstract: Localization technology is a very important topic in Ad Hoc network.The localization arithmetic based on distance is restricted by the devices and power of nodes in Ad Hoc，but in lots of situations there is no need for nodes to know their exact geographical locations.So a kind of localization arithmetic based on directions named flooding-direction localization arithmetic is proposed.Nodes can know their directions relative to a fixed node called sink through this method.Simulation results show that this arithmetic is effective and it can evaluate most of the directions of nodes in the Ad Hoc network.