The present invention relates to crystalline form A of a TLR7 agonist 2-butoxy-7-(4-(pyrrolidin-1-ylmethyl)-benzyl)-5H-pyrrolo[3,2-d]pyrimidin-4-amine (formula I), a method for preparing the crystalline form A, and the use thereof.本發明關於一種TLR7促效劑2-丁氧基-7-(4-(吡咯烷-1-基甲基)苄基)-5H-吡咯并[3,2-d]嘧啶-4-胺(式I)的晶型A、其製備方法及其用途。