Cognitive failure refers to people’s failure to complete simple tasks in daily life based oncognitive errors, resulting in behavioral errors, loneliness and rumination thinking may affect cognitivefailure. In order to explore the effect of loneliness and rumination on cognitive failure and its mechanism,208 college students were tested with loneliness scale, rumination scale and cognitive failure scale. Theresults showed that: (1) After controlling for age, gender and grade, loneliness had a significant positivepredictive effect on cognitive failure; (2) Rumination played a mediating role in the relationship betweenloneliness and cognitive failure. It shows that loneliness not only has a direct effect on cognitive failure,but also ruminating is the internal mechanism of loneliness leading to cognitive failure. In the practiceof psychological counseling to deal with cognitive failure, we can reduce loneliness and rumination, andthen reduce individual cognitive failure.