The present invention relates to a trifluoroacetate salt of a TLR7 agonist 2-butoxy-7-(4-(pyrrolidin-1-ylmethyl)benzyl)-5H-pyrrolo[3,2-d]pyrimidin-4-amine (formula I), crystalline form B of the trifluoroacetate salt, methods for preparing the trifluoroacetate salt and crystalline form B, and uses of the trifluoroacetate salt and crystalline form B.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)的三氟乙酸鹽、其晶型B、其製備方法和用途。