Online learning has gradually become a mainstream teaching method to replace traditional classroom teaching during the COVID-19 pandemic. However, there are some issues such as the lack of theoretical guidance on online learning, and the influencing factors of online learning effect are not well proven. On this basis, this study aimed to construct and test a theoretical model of online learning influencing factors among college students through a mixed-method approach in China to further explore the influencing factors of online learning and the relationship between these influencing factors. First, 130 college students were interviewed from May 2021 to November 2021, and the collected data were coded to a theoretical model through grounded theory. Second, we tested and verified the theoretical model through the analysis of survey data of 225 college students from January 2022 to July 2022. Lastly, the results indicate that the learning expectation influences the learning result through learning quality or learning interaction and their combined effects. These findings can help educators around the world gain insight into the process of online learning and improve the quality of online learning during the COVID-19 pandemic.