Citizen science projects are growing in popularity amongst academia and industry as a means to collect data and solve scientific problems. In the initial stage of citizen science projects, how to motivate participants is a great challenge. Therefore, our study focuses on the cold start phase of citizen science projects in digital humanities domain and conducts an empirical study on the motivation of volunteers' participation in those projects. First, this study proposed main influence factors of volunteers' participation in citizen science projects from three dimensions: platforms, tasks, and volunteers. Then based on S-O-R theory, an empirical model of volunteers' motivations in the cold start stage was established. After that, the authors collected data through questionnaires and tested the hypotheses by SmartPLS 3.0. Results show that factors at the platform dimension and task dimension have an impact on volunteers' cognition and emotion levels, and volunteers' perceived usefulness, self-efficacy, enjoyment and commitment have a positive impact on volunteers' participation intention. Finally, some suggestions are put forward for the practical development of citizen science projects from the perspectives of organization structure, platform design and task design.