Abstract: Occurrence of Welsh onion virosis is widespread ,it is the main reason to cause the yield and the quality to descend; According to the determined result of host range ,appearance of virus particles and pathological ultramicroscopic structure etc.on Welsh onion virosis ,it can ascertain initially that the virus pathogen which infects Welsh onion belongs to the family of potato Y virus (Potyviridae) it is one of provisional members in the genus of potato Y virus (Potyvirus) ,and it can spread virus by its seeds。