We explored the relationship between depression and suicidal ideation among Chinese university freshmen, and also the moderating role of knowledge of suicidal behavior in this relationship. A sample of 1,150 Chinese university freshmen completed the Symptom Checklist-90-Revised to evaluate their depression symptoms, the Suicide Attitude Inventory to evaluate their knowledge of suicidal behavior, and the Youth Self-Report Form to evaluate suicidal ideation. Results showed that knowledge of suicidal behavior had a negative relationship with both depression and suicidal ideation, between which there was a significant positive relationship. This relationship was moderated by knowledge of suicidal behavior. The enhancement of freshmen's knowledge of suicidal behavior may help prevent suicidal ideation among the students, and buffer the effect of depression on suicidal ideation.