Leader-and-follower behaviour is one of the most important behaviours during evacuation, as determining the effect of leader-and-follower behaviour in social networks on crowd evacuation during emergency situations is important for enhancing safety. In this study, four experiments with two social groups involving 81 participants were conducted. Before the experiments, participants were asked to respond to a questionnaire to evaluate individual leadership and to determine the leaders in each social group. In the experiment, the leaders and some randomly selected students were asked to evacuate along a designated route. The influence of the leaders on evacuation patterns was studied by recording the following ratio and following behaviour of the crowd. Furthermore, the effect of smoke on evacuation patterns was studied by releasing smoke on certain paths. Experimental results showed that opinion leaders under normal conditions had a limited influence on the choice of evacuation route among students, despite stable social relationships among students. Instead, external environmental conditions, personal-psychological factors, and vision appeared to play more important roles, and the tendency of participants to congregate was most obvious. Most participants followed the path of those ahead of them and were thus more dependent on group formation. The effect of smoke on evacuation behaviour was not clear. In contrast, the effect of re-entry behaviour on crowd evacuation was more obvious, as most participants tended to follow the re-entry decisions of their peers. Because of personal subconscious habits, advanced scientific planning and drills conducted in advance could be used to greatly improve the emergency evacuation process. These results could also be used to modify evacuation simulation models and contribute to the development of evacuation plans.