diff --git a/pyat/czcore.py b/pyat/czcore.py
index bc60e74..ea4440d 100644
--- a/pyat/czcore.py
+++ b/pyat/czcore.py
@@ -170,7 +170,7 @@ def call_Bellhop_Rays(freq, sd, dr, bathm, ssp, sed, base,azi):
     run_type = 'R'  # incoherently sum beams, see AT docs for more info
     nbeams = 301
     alpha = np.linspace(-15, 15, 2)  # min and max launch angle -20 degrees to 20 degrees
-    box = Box(Zmax, 100)  # bound the region you let the beams go, depth in meters and range in km
+    box = Box(Zmax, Rmax+10)  # bound the region you let the beams go, depth in meters and range in km
     deltas = 0  # length step of ray trace, 0 means automatically choose
     beam = Beam(RunType=run_type, Nbeams=nbeams, alpha=alpha, box=box, deltas=deltas)  # package
     """删除ssp 已修改 8.26"""