Recently, learning-based multi-agent cooperative perception has garnered widespread attention. However, the inherent vulnerabilities of neural networks, combined with the risks posed by cooperative communication as a wide-open backdoor, render these systems highly susceptible to adversarial attacks.Existing attack methods lack stealth as they perturb transmitted information indiscriminately, producing numerous false positives that are readily detected by consensus-based defenses. This paper proposes Pretend Benign (PB), a novel stealthy adversarial attack method that exploits vulnerabilities in cooperative perception to enable the attacker to disguise as a benign cooperator. To achieve this, we first introduce the Attack Region Selection (ARS) module, which divides the perception area into sub-regions based on confidence levels to pinpoint optimal attack locations. Then, we propose Multi-target Adversarial Perturbation Generation (MAPG), which maintains consensus, gain the victim’s trust, and thereby reverse the normal cooperative role of perception. To mitigate the latency in adversarial signal generation and communication, we further propose a real-time attack by predicting future information through historical feature flow. Extensive experiments on the OPV2V and V2XSet datasets demonstrate that PB effectively bypasses state-of-the-art defense methods, underscoring its stealth and efficacy.