X-ray　detection　is　indispensable　in　medical　imaging,　security　inspection,　and　scientific　research.　Green　lead-free　perovskites　have　a　great　prospect　in　the　field　of　X-ray　detection.　Herein,　a　new　layered　hybrid　double　perovskite　(I-BA)(4)AgBiI8　(IAB,　I-BA(+)　is　I-n-butylammonium)　was　rationally　designed.　Strikingly,　it　had　a　large　mu(tau)　product　up　to　similar　to　2.28　x　10(-3)　cm(2)　V-1　and　showed　an　X-ray　response　with　a　superior　sensitivity　of　5.38　mu　C　Gy(air)(-1)　cm(-2).