Citizen science projects are composed of two groups: project initiators (scientists, government agencies, etc.) and project participants (volunteers), whose effective cooperation is key to the effective implementation of projects. Current research focuses on the willingness of public participation, but ignores the prerequisite of cooperation-trust. Based on Trust Building Model, this study proposes main influence factors of volunteers' trust in citizen science projects from four aspects: reputation, website quality, information quality, and institutional structural factors. Through a scenario-based questionnaire, the authors conducted OLS regression on 179 valid data. Data results show that scientist reputation, project initiator reputation, website usability, information publicity, information interaction, and public privacy protection have significant positive impacts on volunteers' trust in citizen science projects, while ease of website use had no significant influence on volunteers' trust.