Bystanders play an essential role in school bullying prevention. This study examines student bystanders' perceptions of severity and willingness to intervene in scenarios involving physical, verbal, relational, and cyberbullying. It focuses on five distinct victim reactions: pretending nothing happened, seeking help, fighting back, crying, and no description as a control group. Using a combination of four bullying types and five victim reaction forms, a survey experiment comprising 20 scenarios (4 × 5) was designed and conducted among primary, middle, and high school students in China (N = 5,075), aged between 8 and 19 years (M = 14.07; SD = 2.10) in 2019. The reactions of victims significantly influenced how bystanders perceived the severity of bullying events and their willingness to intervene. Overall, victims who responded with "crying" evoked a greater intention to intervene among bystanders, while those who "fighting back" or "pretending nothing happened" were seen as less severe. These findings enhance our understanding of bystanders' perspectives on victim responses across different types of school bullying. The outcomes of this study can contribute to the development of more specific antibullying program strategies in practical applications.