Disclosed is a class of 4-pyrimidinediamine small molecular organic compounds or related analogues or pharmaceutically acceptable salts thereof, with the structures thereof as shown in formulae (I)-(VI). Also disclosed are the use of the 4-pyrimidinediamine small molecular organic compounds or pharmaceutical compositions thereof in the preparation of drugs for preventing and/or treating various malignant tumours, autoimmune diseases, inflammation, etc., and the use of same as an inhibitor of B cell lymphokine 6 (BCL6) in the preparation of a drug for preventing and/or treating BCL6-mediated diseases.