Low energy ion implantation technology was used in mutation breeding on arachidonic acid (5, 8, 11, 14−eicosatetraenoic acid, AA) yielding starting strain, Mortierelle alpina N,7,. The results indicate that dispersion of descendants of the N,7, strain implanted with 10keV N,+, (3×10,14, N,+,/cm,2,) was bigger than that in natural division strain. I,49,−N,18, a high−yield AA-producing strain, was screened out by continuous mutagenicity. The biomass, lipid in biomass, AA in lipids of the high−yield strain were 26.3g/L, 33.8%(w/w), and 52.36%(w/w), respectively. The AA content in culture was 4.66g/L, which is 126.2% higher than the control, and its descendiblity was stable. It is concluded that I,49,−N,18 ,is a promising strain for industrialization, and that ion implantation has remarkable mutagenic effect on microorganism.