People increasingly rely on social network sites (SNSs) to find out timely information about crises. Thus, emergency managers are interested in how people participate and how to promote their participation in SNSs after crises. Based on self-determination theory, this study develops a theoretical model to examine the mechanisms through which different types of motivation contribute to various participating behaviors in SNSs after crises. Survey data were collected after the Ya’an earthquake, which occurred in China on April 20, 2013. Our results show that while autonomous motivation is positively related to posting new content about the earthquake, controlled motivation is positively related to commenting on others’ content about the earthquake. Furthermore, perceived autonomy and perceived relatedness are positively related to autonomous motivation. We suggest that emergency managers may want to promote different types of motivations, depending on the specific participating behavior preferred after crises.