The invention discloses a method for automatically generating a code of an ASN.1 decoder. The method comprises the following steps: reading input of an ASN.1 file at first, processing useless comment information and redundant blank characters in the ASN.1 file, analyzing to obtain description of a data type and a structure type of each ASN.1 file, identifying the data type and the structure type to generate corresponding data structure definition, adding the comment information, writing the comment information in a header file, analyzing the header file to obtain data structure definition so as to generate a corresponding source code, and writing the corresponding source code in a source file, so that generation of the code of the ASN.1 decoder is completed. According to the invention, manual coding of staffs is unnecessary to develop; the development cycle is reduced; and code development works of the ASN.1 decoder can be completed accurately and effectively.