This study aimed to analyze the characteristics and risk factors associated with casual sexual behavior among sexually active college students and to contribute to AIDS prevention and control efforts among this demographic. A cross-sectional survey was conducted using a stratified cluster sampling technique. Self-reported sexually active college students were selected as respondents from 11 cities in Zhejiang Province from October 8 to November 30, 2018. A questionnaire was used to collect variables such as demographic information, sexual attitudes, intervention acceptance, and self-efficacy of condom use. Univariate and multivariate analyses were performed. Among 3,771 college students who reported engaging in sexual activity, 675 (17.90%) reported engaging in casual sexual encounters. The multivariate analysis revealed multiple factors associated with casual sexual behavior among students: being male, originating from a city/town, having pursued HIV testing education in the last year, seeking HIV risk self-assessment within the last year, accepting to engage in one-night stand behavior, accepting to partake in commercial sexual activity, having conducted HIV antibody tests within the last year, homosexual partner or homosexual/heterosexual partner, demonstrating self-efficacy in condom usage, and monthly living expenses falling within the range of 1001–1500 yuan. Additionally, students with knowledge that appearance does not determine HIV infection, a proclivity for seeking HIV counseling and testing following high-risk sexual behavior and awareness that the centers for disease control provides HIV diagnosis were found to have significant associations with casual sexual activity. Casual sex is significantly prevalent among college students, with male, students from urban areas, those who accepted to engage in one-night stand behavior and partook in commercial sexual activity demonstrating a higher propensity for such behavior. This tendency can be attributed to several factors including a more liberal sexual attitude, a rudimentary understanding of HIV risk, and a low adoption rate of HIV testing. Therefore, it is imperative to enhance HIV prevention and education among college students.