The invention discloses a preparation method and applications of a solid base catalyst. In the prior art, in the process for preparing p-aminodiphenylamine by using a nitrobenzene method, nitrobenzeneand aniline are subjected to a condensation reaction under the catalytic action of a tetramethylammonium hydroxide aqueous solution to generate a byproduct phenazine. According to the invention, thedisadvantage in the prior art is overcome, and the disadvantage of easy collapse of the alkaline zeolite molecular sieve structure is avoided; tetramethylammonium hydroxide is loaded by adopting active carbon with internal pore channels, such that the by-product phenazine in the process for preparing p-aminodiphenylamine by using the nitrobenzene method is reduced, the conversion rate of nitrobenzene is greater than 99.5%, the selectivity of the target products 4-nitrosodiphenylamine and 4-nitrodiphenylamine is greater than 98.5%, the selectivity of the by-product phenazine is less than 0.20%,the p-aminodiphenylamine raw material consumption is reduced, the quality of the p-aminodiphenylamine product is improved, and the economic benefit of the p-aminodiphenylamine is improved.