Demodex is one of the most common parasites in the human body. It can be classified into demodex folliculorum and demodex brevis based on the parasitic sites. It is an opportunistic pathogenic microorganism, and clinical symptoms may not appear in part of infected people, but the parasite can cause multiple common ocular diseases represented by blepharitis. Its typical symptoms include dry eyes, foreign body sensation in eyes, secretion attached to eyelashes, and ocular surface irritation. The diagnosis of demodex blepharitis should be based on the clinical manifestations and the results of etiological tests. The treatment is related to many kinds of drugs including plant essential oil and physical therapy. At present, diagnosing and treating demodex blepharitis is increasingly sophisticated, but the relationship between demodex infection and its pathogenicity remains unclear. This paper summarizes the current characteristics of demodex and the clinical manifestation, diagnosis, treatment, and existing issues of demodex blepharitis, hoping to provide a reference for future studies in demodex.