The invention relates to a preparation method of electronic grade manganous nitrate for a tantalum capacitor, which includes a. adding crushed and washed manganese metal into nitric acid, stirring the mixture while adding the manganese metal till the manganese metal is completely dissolved and then statically placing the mixture for 10 to 40 minutes; b. conducting coarse filtering on the solution, adjusting the pH value of the solution to be 2 to 4 through nitric acid; and c. heating the solution receiving acid adjustment in vacuum mode to condense the solution to the required ratio, adjusting the pH value of the solution through nitric acid to be 2-5, cooling the solution and conducting fine filtering on the solution to obtain a manganous nitrate solution product. The preparation method can be used for preparing liquid manganous nitrate products in batch in industrial mode to achieve using standard of electronic grade products for the tantalum capacitor. Manganese dioxide produced by the electronic grade manganous nitrate is high in purity, good in crystal structure, good in chemical activity, even and compact in layer, small in particle, firm in adhesion, small in resistivity, low in using unit consumption and low in content of chemical impurities such as iron, calcium, lead, potassium and magnesium, thereby being suitable for serving as high-purity catalyst, oxidant, adsorbent and the like.