•A method based on dose rate was proposed to estimate the expected contaminated people at each assemble point in nuclear accident scenarios, which is more rigorous compared with the other methods using average wind frequency and assembly point orientation.•Combined with public contaminated proportion, population structure and waiting psychology, a public decontamination model based on queuing theory and system dynamics method was proposed for offsite nuclear emergency to quantify the decontamination process and estimate overall time.•A configuration plan for adding devices was provided to meet the time requirement and control the number of waiting queues within the specified threshold efficiently.•The proposed method can help nuclear emergency decision-makers display the decontamination process, estimate the overall time and optimize site configuration plan. Decontamination is an important means to reduce the personnel radioactive contamination under sever nuclear accidents. Public decontamination time estimation with the process simulation is helpful for emergency organizations to improve efficiency. To date, most studies focus on improving personal decontamination technology and decontamination strategies, while research on the overall decontamination process and time estimating is limited. Due to the complex population structure, the unknown contaminated proportion and the complicated psychological emotions, it is hard to quantify the decontamination process and calculate the decontamination time with numerous procedures and diverse facility configurations. Combined with public contaminated proportion, crowd structure and waiting psychology, a public decontamination model based on queuing theory and system dynamics method is established for offsite nuclear emergency to simulate the decontamination process and give an estimate of decontamination time. A hypothetical nuclear leakage accident of Changjiang Nuclear Power Plant in Hainan, China is conducted to simulate the established model. The results show the working status of different facilities at different stages and the changes in waiting queues at different times, which can effectively calculate the duration time of each link and the overall public decontamination progress. A plan for adding devices is provided to meet the decontamination time requirements and control the number of waiting queues within the specified threshold efficiently. The method proposed in this paper could help nuclear emergency decision-makers estimate the public decontamination time, optimize site configuration plans, give guidance on public decontamination procedures and prepare for the subsequent nuclear emergency evacuation.