Provided is an in-vehicle network unicast routing method self-adapted to vehicle density. The routing processes of the in-vehicle network unicast routing method comprise the routing process for mobile nodes and the routing process for static nodes. The routing process for the mobile nodes comprises the following steps of maintaining neighbor state information, sending a report message, sending a departure message, sending a routing request, receiving a routing response and forwarding a message. The routing process for the static nodes comprises the following steps of maintaining the neighbor state information, maintaining a road density value table, maintaining a road time delay table, receiving the routing request, replying a response message and giving a notice of road density changes. When network density is low, the mobile nodes can automatically increase a communication radius and prolong datagram lifetime, so that the success rate is increased within the time delay range required by an application; when network intensity is high, the mobile nodes automatically reduce the communication radius and shorten the datagram lifetime, so that signal collisions in the communication process are reduced while the success rate is increased and time delay is decreased. A good balance is realized between the success rate, time delay and expenditure.