The invention discloses a modified manganese dioxide electrocatalyst, in which calcium elements, silver elements or calcium and silver elements are doped. The invention further discloses a preparation method of the catalyst and application of the catalyst in oxygen evolution reaction of an anode of alkaline electrolysis. The preparation method comprises the steps: (1) dissolving a manganese source and inorganic ammonium salt into solution; (2) performing hydro-thermal treatment of the solution obtained in step (1); (3) separating, washing, drying, thereby obtaining manganese dioxide nano lines; (4) dissolving one or a mixture of inorganic calcium salt and silver into solution; (50 mixing the solution obtained in step (4) and the manganese dioxide nano lines, uniformly stirring, standing and baking to obtain the modified manganese dioxide electrocatalyst. The manganese dioxide nano lines are prepared in a hydro-thermal method; minor miscellaneous elements are introduced to the manganese dioxide nano lines in an equivalent-volume impregnation method so as to modify the manganese dioxide, thus activity of the manganese dioxide in the oxygen evolution reaction of the anode of alkaline electrolysis is improved.