With the continuous integration of wireless communication and intelligent information Technologies, the Internet of Vehicles (IoV) technology has been widely used in Intelligent Transportation Systems (ITS), which has greatly promoted the development of society in the direction of intelligence and information technology. Unfortunately, it is still facing the challenges of spectrum scarcity, ultra-low latency, large-scale connectivity and secure transmission. To this end, we study the covertness performance of multi-antenna assisted ambient backscatter communication (AmBC) Symbiotic ITS. To improve energy efficiency and reduce interference, the optimal antenna of the radio frequency (RF) source is selected to send covert information to covert receiving vehicle via both direct and reflected links with the help of public vehicle, while a monitor vehicle nearby the RF source covertly detects the potential communication behavior between the RF source and covert receiving vehicle. In addition, the RF source transmits a random power signals to interfere with the monitor vehicle’s detection. Specifically, the analytical expressions for the optimal detection threshold and the detection error probability (DEP) of the monitor vehicle are first derived, and then, the closed-form solutions for the outage probability (OP) of the covert receiving vehicle and public vehicle are computed. Then, an optimization scheme based on the maximize effective covert rate (ECR) under covertness and reliability constraints is proposed. Furthermore, the progressivity of OP at high signal-to-noise ratio (SNR) is investigated. The simulation results verify the analysis and prove that: i) the monitor vehicle’s detection performance can be reduced by lowering the power allocated to covert receiving vehicle within a certain range; ii) the OP of covert receiving vehicle is enhanced with the number of antennas; iii) as the RF source’s maximum transmit power increases, the ECR of the considered system increases and converges to a constant; iv) the multi-antenna selection scheme can significantly improve the covertness performance of the considered system.