The present invention relates to a brain-computer interface system and a method for recognizing a conversation intention of a user using the same in addition to inferring the waveform of word sound intended by a user from an imagined speech brainwave associated with a word intended by a user, since the user can intuitively recognize the sentence he/she wants to speak through the imagined speech by classifying words that are most relevant to the imagined speech brainwave of the user in a database in which a word often used by the user or frequently used in a specific situation is stored and by generating a sentence intended by the user by recognizing the words classified in this way, it is possible to perform communication by only thoughts of the user.