Wheat Fusarium crown rot (FCR), mainly caused by Fusarium pseudograminearum, is one of the most important diseases. Some mycoviruses are reported to have a hypovirulence trait and considered as a biocontrol agent for plant fungal diseases. In most cases, mycovirus biological effects have not been explored clearly. In this study, we identified and characterized a novel isolate of double-stranded RNA (dsRNA) mycovirus, Fusarium graminearum dsRNA mycovirus 4 (FgV4), from a new host, an isolate WC9-2 of F. pseudograminearum. The genome of FgV4-WC9-2 includes two dsRNA segments of 2194 bp and 1738 bp. FgV4-WC9-2 dsRNA1 contains a single open reading frame (ORF1), which encodes a protein of 675 amino acids (aa) and has a conserved RNA-dependent RNA polymerase (RdRp) domain. FgV4-WC9-2 dsRNA2 contains two discontinuous ORFs (ORF2-1 and ORF2-2) that code for hypothetical proteins with unknown function. Biological characteristics research has shown that FgV4-WC9-2 infection did not change the colony morphology, but it could significantly decrease colony growth rate. FgV4-WC9-2 could also reduce the sporulation ability, change the conidia size and reduce the pathogenicity of the host to a certain extent. This study is the first to describe a hypovirulence-associated orthocurvulavirus infecting F. pseudograminearum, which has the potential to assist with FCR disease biological management.