Being the revolutionary future networking technology, 6G networks are expected to solve the issue of the drastic data demand and satisfy emerging applications and services. As one of the most feasible nanonetwork paradigms in 6G networks, molecular communication provides opportunities for targeted delivery, which solves nanodevice communication problems. The delivery communication is implemented by the biochemical reaction between the targeted molecule and the released specific Information Molecule (IM). The unprotected characteristic of this communication makes it vulnerable to be attacked on the biological process, adversely affecting the targeted delivery. In this paper, we propose the communication model for targeted delivery under the Bio-Denial of Service (Bio-DoS) attack. We first put forward the concept of the Bio-DoS attack and prove its feasibility. Moreover, we establish the diffusion-based multi-target model for the delivery process considering the combined characteristic of traditional communication and biology features. Simulation results show that the model accurately evaluate the signal receiving and processing in targeted delivery process under attack. This work is of a great significance to analysis the communication performance of the targeted delivery under attack.