A method for selecting an encoding format used for reading a target document, characterized in comprising: selecting at least two encoding formats as reference encoding formats from a set of multiple encoding formats; reading each reference document with each reference encoding format and determining a disorder code pattern, comprising: reading the reference document with the reference encoding format to obtain a disorder code string, removing invalid determination codes in the disorder code string and obtaining valid determination codes, counting the number of times disorder codes appear in the valid determination codes to obtain a disorder code pattern, in which all disorder codes that appear a number of times larger than a first threshold specified in advance, are stored as a disorder code pattern, the invalid determination codes being English characters, numbers and blank characters, and the valid determination codes being all of other codes except for the invalid determination codes; reading the target document with at least two encoding formats; for each encoding format, comparing data generated when reading the target document with this encoding format and the disorder code patterns determined for this encoding format in order to determine disorder codes generated when reading the target document with this encoding format; counting a proportion of disorder codes generated when reading the target document with each encoding format and selecting an encoding format having a proportion of disorder codes less than a second predetermined threshold as the encoding format to be used for reading the target document. selecting at least two encoding formats as reference encoding formats from a set of multiple encoding formats; reading each reference document with each reference encoding format and determining a disorder code pattern, comprising: reading the reference document with the reference encoding format to obtain a disorder code string, removing invalid determination codes in the disorder code string and obtaining valid determination codes, counting the number of times disorder codes appear in the valid determination codes to obtain a disorder code pattern, in which all disorder codes that appear a number of times larger than a first threshold specified in advance, are stored as a disorder code pattern, the invalid determination codes being English characters, numbers and blank characters, and the valid determination codes being all of other codes except for the invalid determination codes; reading the target document with at least two encoding formats; for each encoding format, comparing data generated when reading the target document with this encoding format and the disorder code patterns determined for this encoding format in order to determine disorder codes generated when reading the target document with this encoding format; counting a proportion of disorder codes generated when reading the target document with each encoding format and selecting an encoding format having a proportion of disorder codes less than a second predetermined threshold as the encoding format to be used for reading the target document. reading the reference document with the reference encoding format to obtain a disorder code string, removing invalid determination codes in the disorder code string and obtaining valid determination codes, counting the number of times disorder codes appear in the valid determination codes to obtain a disorder code pattern, in which all disorder codes that appear a number of times larger than a first threshold specified in advance, are stored as a disorder code pattern, the invalid determination codes being English characters, numbers and blank characters, and the valid determination codes being all of other codes except for the invalid determination codes; reading the target document with at least two encoding formats; for each encoding format, comparing data generated when reading the target document with this encoding format and the disorder code patterns determined for this encoding format in order to determine disorder codes generated when reading the target document with this encoding format; counting a proportion of disorder codes generated when reading the target document with each encoding format and selecting an encoding format having a proportion of disorder codes less than a second predetermined threshold as the encoding format to be used for reading the target document.