With the rapid development of automotive intelligence and connectivity, the in-vehicle CAN networks system is vulnerable for the lack of encryption and authentication scheme. To prevent unauthorized access and secure the in-vehicle CAN network, only authorized ECUs (Electric Control Units) can communicate with each other. An ECU authentication method based on Physically Unclonable Functions (PUF) is presented. To ensure applicability in vehicle CAN networks with limited resources, a PUF circuit with lower resource consumption and reduced temperature sensitivity is designed. The output of the designed PUF circuit is unpredictable and unclonable, providing the ECU with unique identity information for authentication to the Domain Control Unit (DCU). The designed PUF circuit is implemented on a Field Programmable Gate Array (FPGA) platform and successfully integrated into a CAN network prototype system. Experimental results show that the proposed authentication method has good performance in terms of resource consumption and stability.