Abstract: The objective of this paper is to investigate the cytogenetic basis for origin of triploid apomictic Boehmeria tricuspis. We developed a study on the meiosis of PMC between the triploid apomictic B.tricuspis and the diploid sexual B.tricuspis. Rich trivalents were found in the PMC meiosis of triploid apomictic B.tricuspis showed it’s a autotriploid；In the sexual B.tricuspis,the PMC meiosis usually be normal.But a few were abnormal and some of their behavior maybe led to the occurrence of 2n gamete. The fusion of 2n gamete and n gamete may led to autotriploid apomictic plants. This is the cytogenetic basic event for the origin of triploid apomictic B.tricuspis.