A method for preparing D, L-methionine, comprising the following steps: preparing a 5-(β-methylthioethyl)glycolyurea reaction fluid by using 3-methylthio propionaldehyde, KCN and NH 4 HCO 3 solutions as raw materials for continuous reaction in the tubular reactor that is gradually heated; decompressing the 5-(β-methylthioethyl)glycolyurea reaction fluid to separate NH3 and CO2 for delivery to another tubular reactor for decomposition and saponification to obtain a saponification reaction fluid; eliminating NH3 and CO2 produced during saponification through desorption of the saponification fluid to obtain a D,L-methionine potassium solution; obtaining a NH4HCO3 solution through water spray and absorption of NH3 and CO2 as separated in steps and, and directly using use the NH4HCO3 solution as a material for preparation of the 5-(β-methylthioethyl)glycolyurea reaction fluid in step; cooling down the D,L-methionine potassium solution in step, and then using an organic solvent for reversed and continuous extraction; directly using an organic solvent recycled through distillation of an organic solvent layer for reversed and continuous extraction; raffinate produced by distillation being treated as waste fluid; delivering water that is produced through counter-current and continuous extraction in step to a continuous crystallizer, simultaneously delivering CO 2 gas to the continuous crystallizer for acidification to control pH value of reaction fluid in the continuous crystallizer at 6-9, and then obtaining a crystallization intermixture; separating solid and liquid in the crystallization intermixture to obtain crude D,L-methionine product and a crystallization mother solution; washing crude D,L-methionine product with water for solid-liquid separation to obtain a filter cake of D,L-methionine and washing filtrate; drying the filter cake of D,L-methionine under the protection of inert gas to obtain D,L-methionine product; combining the crystallization mother solution and the washing filtrate from step for delivery to a decomposition column to fully decompose KHCO 3 into K 2 CO 3 for release of CO 2 gas; released CO 2 gas that is subjected to compression is delivered to continuous crystallizer for acidification and crystallization; using the K 2 CO 3 containing mother solution as obtained in step for absorption of HCN gas to prepare a KCN solution that is the material for preparation of 5-(β-methylthioethyl)glycolyurea in step. preparing a 5-(β-methylthioethyl)glycolyurea reaction fluid by using 3-methylthio propionaldehyde, KCN and NH 4 HCO 3 solutions as raw materials for continuous reaction in the tubular reactor that is gradually heated; decompressing the 5-(β-methylthioethyl)glycolyurea reaction fluid to separate NH3 and CO2 for delivery to another tubular reactor for decomposition and saponification to obtain a saponification reaction fluid; eliminating NH3 and CO2 produced during saponification through desorption of the saponification fluid to obtain a D,L-methionine potassium solution; obtaining a NH4HCO3 solution through water spray and absorption of NH3 and CO2 as separated in steps and, and directly using use the NH4HCO3 solution as a material for preparation of the 5-(β-methylthioethyl)glycolyurea reaction fluid in step; cooling down the D,L-methionine potassium solution in step, and then using an organic solvent for reversed and continuous extraction; directly using an organic solvent recycled through distillation of an organic solvent layer for reversed and continuous extraction; raffinate produced by distillation being treated as waste fluid; delivering water that is produced through counter-current and continuous extraction in step to a continuous crystallizer, simultaneously delivering CO 2 gas to the continuous crystallizer for acidification to control pH value of reaction fluid in the continuous crystallizer at 6-9, and then obtaining a crystallization intermixture; separating solid and liquid in the crystallization intermixture to obtain crude D,L-methionine product and a crystallization mother solution; washing crude D,L-methionine product with water for solid-liquid separation to obtain a filter cake of D,L-methionine and washing filtrate; drying the filter cake of D,L-methionine under the protection of inert gas to obtain D,L-methionine product; combining the crystallization mother solution and the washing filtrate from step for delivery to a decomposition column to fully decompose KHCO 3 into K 2 CO 3 for release of CO 2 gas; released CO 2 gas that is subjected to compression is delivered to continuous crystallizer for acidification and crystallization; using the K 2 CO 3 containing mother solution as obtained in step for absorption of HCN gas to prepare a KCN solution that is the material for preparation of 5-(β-methylthioethyl)glycolyurea in step.