In the field of Internet of Vehicles (IoV), vehicles are now required to not only provide quick transportation capability, but also support different network services. These services generally need reliable and efficient data exchanges and disseminations. However, due to the inherent features of IoV, e.g. fast topology change, varying density distribution, have brought great challenges for the success of these services. In order to solve above issues, this paper presents a slotted data dissemination scheme based on the moving direction of vehicles named as SAMD (A Slot Assignment scheme based on Moving Directions of vehicles). First, the super-frame used for carrying payload, is slotted and divided into left and right time slots set, respectively. After that, each vehicle competes and/or reserves the time slots using slotted CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) and/or TDMA (Time Division Multiple Access) according to its moving direction. Numerical results show that our protocol could reduce the probability of merging collisions of time slots and increases the packet delivery ratio, compared to the classic ADHOC and VeMAC protocols.