The present invention provides a method for preparing a solid acrylamide alkyl sulfonate. Said method comprises: reacting 2-acrylamido-2-methylpropanesulfonic acid and analogs thereof with an alkaline substance in a solvent. The 2-acrylamido-2-methylpropanesulfonic acid and the analogs thereof and the alkaline substance are significant excess with respect to the solvent, so that the amount of the resulting acrylamido alkyl sulfonate exceeds the solubility under the reaction condition. The acrylamido alkyl sulfonate can be continuously generated and directly massively precipitated, and the precipitated solid product, i.e. the product, is collected. The method of the present invention can greatly improve production efficiency of products, save time, reduce cost, and easy to operate by leaving out the re-crystallization step and the like in the prior art.