According to bioecological theory, the development of college students’ social responsibility is affected by the cumulative effect of ecological risks. However, research on the impact of cumulative ecological risk on social responsibility and its potential mechanisms are still lacking. Carol Gilligan (1982) proposed that the ethics of care and justice are like two related but independent melodies, which together constitute the whole of moral psychology. However, despite being an important part of moral psychology, social responsibility has rarely been investigated empirically with regards to the psychological mechanisms of justice and caring orientation. Therefore, the current study had 1607 college students complete questionnaires regarding cumulative ecological risk, social responsibility, belief in a just world, and empathy, aiming to explore the impact of cumulative ecological risk on college students’ sense of social responsibility and the mediating roles of belief in a just world and empathy. Results showed that: (1) cumulative ecological risk was significantly negatively correlated with college students’ sense of social responsibility, belief in a just world, and empathy, whereas social responsibility, belief in a just world, and empathy were significantly positively correlated; (2) belief in a just world and empathy played mediating roles in the relationship between cumulative ecological risk and social responsibility. The results also showed that the development of college students’ sense of social responsibility was affected by the cumulative ecological risk from various directions; this influence was also seen to play a role in the motivation system of social responsibility through the ethics of care with empathy as the important part, as well as through the ethics of justice. The results suggest that we should reduce the ecological risks at their source, and improve and consolidate students’ social support systems; moreover, we should not only enhance college students’ sense of mission and responsibility to consciously maintain social justice order, but also adopt empathy training as a part of the curriculum to improve students’ empathy at the individual level.