According to the humility-helping hypothesis, the question of whether humility affects altruistic behavior has received extensive attention. However, researchers have not established many links between humility and international altruism. The study explored humility as a stable personality trait and assessed whether it encouraged international altruism. It also examined the underlying mechanism between the foregoing relationship. We recruited 940 college students aged 18–23 to participate in an anonymous online survey and obtained 929 data points. The results showed that humility has a direct impact on international altruism. They largely supported the theoretical framework of the humility-helping hypothesis on the inter-group level. We also addressed the mediating effect that identification with all humanity had in the relationship between humility and international altruism. The findings showed that two forms of empathy (empathy and group empathy) have a moderating effect, indicating that different forms of empathy should be more emphasized in different social situations. Taken together, the results show that developing people’s humility and helping them to identify with all humanity are key to promoting inter-group altruism, especially for those who can empathize with other people or groups.