Abstract: The design and calculation elements of the single anode magnetron injection gun for gyrotron is researched. with 8 mm and the third-harmoric gyrotron of the casing by the permanent magnet for examples. The Numerical calculation and optimization is carried out by use of an self-redact electron trajectory code, The space charge effects and the velocity spreads is discussed. Lastly, The optimal parameters with electrode shapes and electronic trajectory was obtained. The single anode magnetron injection gun was employed experiments and researches for 8 mm and the third-harmoric gyrotron of the casing by the permanent magnet. The results was all right.