Abstract: Piwi-interacting RNA (PiRNA), a newly identified class of small non-coding RNA whose length are 26-31nt, can combine with PIWI proteins to regulate transcription gene silencing process, heterochromatin modifications and maintain germline and stem cell function, etc.. In recent years, the study found the abnormal expression of piRNA in various cancers is closely related to the occurrence and spread of tumor and the prognosis of disease. piRNA is expected to become a new target for clinical diagnosis and treatment of tumor. This paper aims to explore the mechanism of piRNA in cancer and provide new ideas for clinical diagnosis and treatment hopefully.